Then, on the evening of the fourteenth day of the month, the whole community of Israel will kill the animals.

From the evening of the fourteenth day of the first month to the evening of the twenty-first day, you must not eat any bread made with yeast.

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.)