2 Chronicles 30:3

since they could not celebrate it at that time, because the priests had not consecrated themselves in sufficient numbers, nor had the people been gathered to Jerusalem.

2 Chronicles 29:34

But the priests were too few, so that they were unable to skin all the burnt offerings; therefore their brothers the Levites helped them until the work was completed and until the other priests had consecrated themselves. For the Levites were more conscientious to consecrate themselves than the priests.

Exodus 12:6

You shall keep it until the fourteenth day of the same month, then the whole assembly of the congregation of Israel is to kill it at twilight.

Exodus 12:18

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.

2 Chronicles 29:17

Now they began the consecration on the first day of the first month, and on the eighth day of the month they entered the porch of the Lord. Then they consecrated the house of the Lord in eight days, and 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

Exodus 12:6
You shall keep it until the fourteenth day of the same month, then the whole assembly of the congregation of Israel is to kill it at twilight.

Because

2 Chronicles 29:34
But the priests were too few, so that they were unable to skin all the burnt offerings; therefore their brothers the Levites helped them until the work was completed and until the other priests had consecrated themselves. For the Levites were more conscientious to consecrate themselves than the priests.