In the Wilderness of Sinai, the LORD had instructed Moses about celebrating a Second Passover at twilight on the 14th day of second month if the people were not ready to observe it on the first month.

In 2 Chronicles 29 to 31, there was a delayed Passover in the first year reign of King Hezekiah when he was 25 years old. There was a period of 16 days used for temple cleaning starting from the first day and ending on the sixteenth day of the first month. Because the people were not ready for the Passover on the 14th day of the first month, a delay of one month was observed according to what the LORD had instructed Moses in Numbers 9.

As the king commanded the priests and the Levites, they began to make the Temple ritually clean, according to the Law of the LORD. The priests went inside the Temple to purify it, and they carried out into the Temple courtyard everything that was ritually unclean. From there the Levites took it all outside the city to Kidron Valley. The whole cleaning and sanctification process took 16 days! There was so much unclean and unholy things and rubbish in the house of the LORD!

As the Passover was not observed on the first month, it was postponed to the 14th day of the second month. Even after the delay, many still were not ready to observe the Passover. Messengers were sent throughout the land to invite the people of God to come to Jerusalem to observe the delayed Passover. Many refused; some even scorned those runners who carried the invitation and message.

Herein is the biblical record (NKJV):

2 Chronicles 29

1. Hezekiah became king when he was twenty-five years old, and he reigned twenty-nine years in Jerusalem. His mother's name was Abijah the daughter of Zechariah.
2. And he did what was right in the sight of the LORD, according to all that his father David had done.
3. In the first year of his reign, in the first month, he opened the doors of the house of the LORD and repaired them.
4. Then he brought in the priests and the Levites, and gathered them in the East Square,
5. and said to them: "Hear me, Levites! Now sanctify yourselves, sanctify the house of the LORD God of your fathers, and carry out the rubbish from the holy place.
6. "For our fathers have trespassed and done evil in the eyes of the LORD our God; they have forsaken Him, have turned their faces away from the dwelling place of the LORD, and turned their backs on Him.
7. "They have also shut up the doors of the vestibule, put out the lamps, and have not burned incense or offered burnt offerings in the holy place to the God of Israel.
8. "Therefore the wrath of the LORD fell upon Judah and Jerusalem, and He has given them up to trouble, to desolation, and to jeering, as you see with your eyes.
9. "For indeed, because of this our fathers have fallen by the sword; and our sons, our daughters, and our wives are in captivity.
10. "Now it is in my heart to make a covenant with the LORD God of Israel, that His fierce wrath may turn away from us.
11. "My sons, do not be negligent now, for the LORD has chosen you to stand before Him, to serve Him, and that you should minister to Him and burn incense."
12. Then these Levites arose (went into action <TLB>): Mahath the son of Amasai and Joel the son of Azariah, of the sons of the Kohathites; of the sons of Merari, Kish the son of Abdi and Azariah the son of Jehalelel; of the Gershonites, Joah the son of Zimmah and Eden the son of Joah;
13. of the sons of Elizaphan, Shimri and Jeiel; of the sons of Asaph, Zechariah and Mattaniah;
14. of the sons of Heman, Jehiel and Shimei; and of the sons of Jeduthun, Shemaiah and Uzziel.
15. And they gathered their brethren, sanctified themselves, and went according to the commandment of the king, at the words of the LORD, to cleanse the house of the LORD.
16. Then the priests went into the inner part of the house of the LORD to cleanse it, and brought out all the debris that they found in the temple of the LORD to the court of the house of the LORD. And the Levites took it out and carried it to the Brook Kidron.
17. Now they began to sanctify on the first day of the first month, and on the eighth day of the month they came to the vestibule of the LORD (Note: the outer court). Then they sanctified the house of the LORD in eight days, and on the sixteenth day of the first month they finished. (Note: The 14th day of the first month is the beginning of the Passover. The entire cleaning job was completed in sixteen days.)
18. Then they went in to King Hezekiah and said, "We have cleansed all the house of the LORD, the altar of burnt offerings with all its articles, and the table of the showbread with all its articles.
19. "Moreover all the articles which King Ahaz in his reign had cast aside in his transgression we have prepared and sanctified; and there they are, before the altar of the LORD."
20. Then King Hezekiah rose early, gathered the rulers of the city, and went up to the house of the LORD.
21. And they brought seven bulls, seven rams, seven lambs, and seven male goats for a sin offering for the kingdom, for the sanctuary, and for Judah. Then he commanded the priests, the sons of Aaron, to offer them on the altar of the LORD.
22. So they killed the bulls, and the priests received the blood and sprinkled it on the altar. Likewise they killed the rams and sprinkled the blood on the altar. They also killed the lambs and sprinkled the blood on the altar.
23. Then they brought out the male goats for the sin offering before the king and the assembly, and they laid their hands on them.
24. And the priests killed them; and they presented their blood on the altar as a sin offering to make an atonement for all Israel, for the king commanded that the burnt offering and the sin offering be made for all Israel.
25. And he stationed the Levites in the house of the LORD with cymbals, with stringed instruments, and with harps, according to the commandment of David, of Gad the king's seer, and of Nathan the prophet; for thus was the commandment of the LORD by his prophets.
26. The Levites stood with the instruments of David, and the priests with the trumpets.
27. Then Hezekiah commanded them to offer the burnt offering on the altar. And when the burnt offering began, the song of the LORD also began, with the trumpets and with the instruments of David king of Israel.
28. So all the assembly worshiped, the singers sang, and the trumpeters sounded; all this continued until the burnt offering was finished.
29. And when they had finished offering, the king and all who were present with him bowed and worshiped.
30. Moreover King Hezekiah and the leaders commanded the Levites to sing praise to the LORD with the words of David and of Asaph the seer. So they sang praises with gladness, and they bowed their heads and worshiped.
31. Then Hezekiah answered and said, "Now that you have consecrated yourselves to the LORD, come near, and bring sacrifices and thank offerings into the house of the LORD." So the assembly brought in sacrifices and thank offerings, and as many as were of a willing heart brought burnt offerings.
32. And the number of the burnt offerings which the assembly brought was seventy bulls, one hundred rams, and two hundred lambs; all these were for a burnt offering to the LORD.
33. The consecrated things were six hundred bulls and three thousand sheep.
34. But the priests were too few, so that they could not skin all the burnt offerings; therefore their brethren the Levites helped them until the work was ended and until the other priests had sanctified themselves, for the Levites were more diligent in sanctifying themselves than the priests.
35. Also the burnt offerings were in abundance, with the fat of the peace offerings and with the drink offerings for every burnt offering. So the service of the house of the LORD was set in order.
36. Then Hezekiah and all the people rejoiced that God had prepared the people, since the events took place so suddenly.

2 Chronicles 30

1. And Hezekiah sent to all Israel and Judah, and also wrote letters to Ephraim and Manasseh, that they should come to the house of the LORD at Jerusalem, to keep the Passover to the LORD God of Israel.
2. For the king and his leaders and all the congregation in Jerusalem had agreed to keep the Passover in the second month.
3. For they could not keep it at the regular time, because a sufficient number of priests had not consecrated themselves, nor had the people gathered together at Jerusalem.
4. And the matter pleased the king and all the assembly.
5. So they resolved to make a proclamation throughout all Israel, from Beersheba to Dan, that they should come to keep the Passover to the LORD God of Israel at Jerusalem, since they had not done it for a long time in the prescribed manner.
6. Then the runners went throughout all Israel and Judah with the letters from the king and his leaders, and spoke according to the command of the king: "Children of Israel, return to the LORD God of Abraham, Isaac, and Israel; then He will return to the remnant of you who have escaped from the hand of the kings of Assyria.
7. "And do not be like your fathers and your brethren, who trespassed against the LORD God of their fathers, so that He gave them up to desolation, as you see.
8. "Now do not be stiff necked, as your fathers were, but yield yourselves to the LORD; and enter His sanctuary, which He has sanctified forever, and serve the LORD your God, that the fierceness of His wrath may turn away from you.
9. "For if you return to the LORD, your brethren and your children will be treated with compassion by those who lead them captive, so that they may come back to this land; for the LORD your God is gracious and merciful, and will not turn His face from you if you return to Him."
10. So the runners passed from city to city through the country of Ephraim and Manasseh, as far as Zebulun; but they laughed at them and mocked them.
11. Nevertheless some from Asher, Manasseh, and Zebulun humbled themselves and came to Jerusalem.
12. Also the hand of God was on Judah to give them singleness of heart to obey the command of the king and the leaders, at the word of the LORD.
13. Now many people, a very great assembly, gathered at Jerusalem to keep the Feast of Unleavened Bread in the second month.
14. They arose and took away the altars that were in Jerusalem, and they took away all the incense altars and cast them into the Brook Kidron.
15. Then they slaughtered the Passover lambs on the fourteenth day of the second month. The priests and the Levites were ashamed, and sanctified themselves, and brought the burnt offerings to the house of the LORD.
16. They stood in their place according to their custom, according to the Law of Moses the man of God; the priests sprinkled the blood received from the hand of the Levites.
17. For there were many in the assembly who had not sanctified themselves; therefore the Levites had charge of the slaughter of the Passover lambs for everyone who was not clean, to sanctify them to the LORD.
18. For a multitude of the people, many from Ephraim, Manasseh, Issachar, and Zebulun, had not cleansed themselves, yet they ate the Passover contrary to what was written. But Hezekiah prayed for them, saying, "May the good LORD provide atonement for everyone
19. who prepares his heart to seek God, the LORD God of his fathers, though he is not cleansed according to the purification of the sanctuary."
20. And the LORD listened to Hezekiah and healed the people.
21. So the children of Israel who were present at Jerusalem kept the Feast of Unleavened Bread seven days with great gladness; and the Levites and the priests praised the LORD day by day, singing to the LORD, accompanied by loud instruments.
22. And Hezekiah gave encouragement to all the Levites who taught the good knowledge of the LORD; and they ate throughout the feast seven days, offering peace offerings and making confession to the LORD God of their fathers.
23. Then the whole assembly agreed to keep the feast another seven days, and they kept it another seven days with gladness. (Note: This Delayed Passover was celebrated for two weeks instead of one.)
24. For Hezekiah king of Judah gave to the assembly a thousand bulls and seven thousand sheep, and the leaders gave to the assembly a thousand bulls and ten thousand sheep; and a great number of priests sanctified themselves.
25. The whole assembly of Judah rejoiced, also the priests and Levites, all the assembly that came from Israel, the sojourners who came from the land of Israel, and those who dwelt in Judah.
26. So there was great joy in Jerusalem, for since the time of Solomon the son of David, king of Israel, there had been nothing like this in Jerusalem.
27. Then the priests, the Levites, arose and blessed the people, and their voice was heard; and their prayer came up to His holy dwelling place, to heaven.

2 Chronicles 31

1. Now when all this was finished, all Israel who were present went out to the cities of Judah and broke the sacred pillars in pieces, cut down the wooden images, and threw down the high places and the altars-- from all Judah, Benjamin, Ephraim, and Manasseh-- until they had utterly destroyed them all. Then all the children of Israel returned to their own cities, every man to his possession.
2. And Hezekiah appointed the divisions of the priests and the Levites according to their divisions, each man according to his service, the priests and Levites for burnt offerings and peace offerings, to serve, to give thanks, and to praise in the gates of the camp of the LORD.
3. The king also appointed a portion of his possessions for the burnt offerings: for the morning and evening burnt offerings, the burnt offerings for the Sabbaths and the New Moons and the set feasts, as it is written in the Law of the LORD.
4. Moreover he commanded the people who dwelt in Jerusalem to contribute support for the priests and the Levites, that they might devote themselves to the Law of the LORD.
5. As soon as the commandment was circulated, the children of Israel brought in abundance the firstfruits of grain and wine, oil and honey, and of all the produce of the field; and they brought in abundantly the tithe of everything.
6. And the children of Israel and Judah, who dwelt in the cities of Judah, brought the tithe of oxen and sheep; also the tithe of holy things which were consecrated to the LORD their God they laid in heaps.
7. In the third month they began laying them in heaps, and they finished in the seventh month.
8. And when Hezekiah and the leaders came and saw the heaps, they blessed the LORD and His people Israel.
9. Then Hezekiah questioned the priests and the Levites concerning the heaps.
10. And Azariah the chief priest, from the house of Zadok, answered him and said, "Since the people began to bring the offerings into the house of the LORD, we have had enough to eat and have plenty left, for the LORD has blessed His people; and what is left is this great abundance."
11. Now Hezekiah commanded them to prepare rooms in the house of the LORD, and they prepared them.
12. Then they faithfully brought in the offerings, the tithes, and the dedicated things; Cononiah the Levite had charge of them, and Shimei his brother was the next.
13. Jehiel, Azaziah, Nahath, Asahel, Jerimoth, Jozabad, Eliel, Ismachiah, Mahath, and Benaiah were overseers under the hand of Cononiah and Shimei his brother, at the commandment of Hezekiah the king and Azariah the ruler of the house of God.
14. Kore the son of Imnah the Levite, the keeper of the East Gate, was over the freewill offerings to God, to distribute the offerings of the LORD and the most holy things.
15. And under him were Eden, Miniamin, Jeshua, Shemaiah, Amariah, and Shecaniah, his faithful assistants in the cities of the priests, to distribute allotments to their brethren by divisions, to the great as well as the small.
16. Besides those males from three years old and up who were written in the genealogy, they distributed to everyone who entered the house of the LORD his daily portion for the work of his service, by his division,
17. and to the priests who were written in the genealogy according to their father's house, and to the Levites from twenty years old and up according to their work, by their divisions,
18. and to all who were written in the genealogy-- their little ones and their wives, their sons and daughters, the whole company of them-- for in their faithfulness they sanctified themselves in holiness.
19. Also for the sons of Aaron the priests, who were in the fields of the common-lands of their cities, in every single city, there were men who were designated by name to distribute portions to all the males among the priests and to all who were listed by genealogies among the Levites.
20. Thus Hezekiah did throughout all Judah, and he did what was good and right and true before the LORD his God.
21. And in every work that he began in the service of the house of God, in the law and in the commandment, to seek his God, he did it with all his heart. So he prospered.

Special Notes:
King Hezekiah's mother was Abijah the daughter of Zechariah.

Interestingly, the forerunner of our Lord is John the Baptist. His dad, Zechariah is a priest who belonged to the priestly division of Abijah; and his mother Elizabeth was also a descendant of Aaron. Both of them were upright in the sight of God, observing all the Lord's commandments and regulations blamelessly (Luke 1:5-7).