Exodus 12:17
And ye shall observe the feast of unleavened bread; for in this selfsame day have I brought your armies out of the land of Egypt: therefore shall ye observe this day in your generations by an ordinance for ever.
And ye shall observe the feast of unleavened bread,.... Which was a distinct feast from the passover feast; for though at that unleavened bread was eaten, it was kept but one night, this seven days; and it is repeated that it might be taken notice of, and the rather, as it was to be observed in all ages as long as the Jewish economy lasted; the reason of which follows:
for in this selfsame day have I brought your armies out of the land of Egypt; which, though not already done, was just on doing, and was certain; and besides, it respects the day when it should come about another year: by their "armies" are meant the tribes of Israel, not so much for their military force, for as yet they were an unarmed people, but for their numbers, which were sufficient to make several considerable armies, and for their order and ease, and their being without any fear of the enemy, in which they marched out of Egypt:
therefore shall ye observe this day in your generations by an ordinance for ever; according to the rules given, with the same exactness, strictness, and constancy, as the first of the passover, and as long as that continued; See Gill on "Exodus 12:14".