They could not celebrate it at the regular time because not enough priests had performed the ceremonies to make themselves holy and the people had not gathered in Jerusalem.

Since there were not enough priests to kill all these animals, the Levites helped them until the work was finished. By then more priests had made themselves ritually clean. The Levites were more faithful in keeping ritually clean than the priests were.

Take care of it until the fourteenth day of this month. Then at dusk, all the assembled people from the community of Israel must slaughter their animals.

In the first month, on the fourteenth day of the month at evening, you shall eat unleavened bread, until the twenty-first day of the month at evening.

They started on the first day of the first month. On the eighth day they went into Jehovah's entrance hall. For eight days they performed the ceremonies to make Jehovah's Temple holy. They finished on the sixteenth day of the first month.

Treasury of Scripture Knowledge

Summary

For they could not keep it at that time, because the priests had not sanctified themselves sufficiently, neither had the people gathered themselves together to Jerusalem.

At that time

Bible References

At that time

Take care of it until the fourteenth day of this month. Then at dusk, all the assembled people from the community of Israel must slaughter their animals.

Because

Since there were not enough priests to kill all these animals, the Levites helped them until the work was finished. By then more priests had made themselves ritually clean. The Levites were more faithful in keeping ritually clean than the priests were.
All Translations
A Conservative Version
American Bible Union New Testament
American Standard Version
Amplified
An Understandable Version
Anderson New Testament
Bible in Basic English
Common New Testament
Daniel Mace New Testament
Darby Translation
Emphatic Diaglott Bible
Godbey New Testament
Goodspeed New Testament
Holman Bible
International Standard Version
John Wesley New Testament
Julia Smith Translation
King James 2000
King James Version
Lexham Expanded Bible
Living Oracles New Testament
Modern King James verseion
Modern Spelling Tyndale-Coverdale
Moffatt New Testament
Montgomery New Testament
NET Bible
New American Standard Bible
New Heart English Bible
Noyes New Testament
Sawyer New Testament
The Emphasized Bible
Thomas Haweis New Testament
Twentieth Century New Testament
Webster
Weymouth New Testament
Williams New Testament
World English Bible
Worldwide English (NT)
Worrell New Testament
Worsley New Testament
Youngs Literal Translation