John Calvin Commentary Leviticus 23:4

"These are the set feasts of Jehovah, even holy convocations, which ye shall proclaim in their appointed season." — Leviticus 23:4 (ASV)

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 mentioned, the mystery of which I have connected, not without reason, to the First Commandment, for its institution was explained there, since it acted as a restraint on the people from falling away to foreign gods. In that rite, they were initiated into the service of God, so that they might abandon all the superstitions of the Gentiles and submit to 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 appropriately listed among the other festivals. And surely it is clear that the Fourth Commandment had no other purpose or function except to exercise the people in the service of God; but since the killing of the lamb represented the grace of adoption by which God had bound them to Himself, it was necessary to connect it to the First Commandment. Let my readers, therefore, now be content with the other part, that is, that its annual celebration was an aid to the Israelites' perpetual recollection of their redemption.