John Calvin on Leviticus 23:4-9

4. These are the feasts of the Lord. The other festivals which Moses here enumerates have an affinity to the Sabbath. In the first place the Passover is put, the mystery of which I have annexed, not without reason, to the First Commandment, for its institution was there explained, inasmuch as it acted as a restraint on the people from falling away to strange gods. In that rite they were initiated to the service of God, that they might abandon all the superstitions of the Gentiles, and acquiesce in the pure instruction of the Law. The Passover, therefore, in itself was a supplement to the First Commandment; yet the day recurring from year to year is fitly enumerated amongst the other festivals. And surely it is plain that the Fourth Commandment had no other object or use except to exercise the people in the service of God; but since the killing of the lamb represented the grace of adoption whereby God had bound them to Himself, it was necessary to annex it to the First Commandment. Let my readers therefore now be content with the other part, i.e., that its annual celebration was a help to the perpetual recollection by the Israelites of their redemption.