Exodus 13:3

3.And Moses said unto the people. He repeats what he had said more at length in the foregoing chapter, respecting the unleavened bread, not so much to instruct as to exhort them; for he had already expressed the matter with so much clearness, that there was no need of further explanation; but it was useful to stimulate them, that they might devote themselves with greater zeal to their duty, and especially lest, after a longer lapse of time, their ardor should, as usual, gradually abate. He therefore exhorts them, that after they cane into the land, they should diligently observe what he had before commanded. And from the context here, it is plain that the two commands as to the sanctifying the first-born, and celebrating the passover, had the same object, viz., that their deliverance should retain the elect people in the special service of the true God.