John Calvin Commentary Deuteronomy 16:1

"Observe the month of Abib, and keep the passover unto Jehovah thy God; for in the month of Abib Jehovah thy God brought thee forth out of Egypt by night." — Deuteronomy 16:1 (ASV)

Observe the month Abib. The purpose for which God instituted the Passover has already been shown in the exposition of the First Commandment. Since it was a symbol of redemption, and in that ceremony the people engaged in the pure worship of the One God, so as to acknowledge Him as their only Father and distinguish Him from all idols, I thought that the actual slaying of the lamb should be introduced among the Supplements to the First Commandment.

It only remains for us to speak here of what relates to the Sabbath. This, then, was the first solemn day on which God intended His people to rest and go up to Jerusalem, forsaking all their business. But mention is made here not only of the Paschal Lamb, but He also commands sheep and oxen to be slain in the place which He would choose.

In these words He signifies that on that day a holy convocation was to be held. This is expressed more clearly soon after (for I have already given the two intermediate verses in the institution of the Passover itself). He therefore prohibits them from slaying the Passover separately in their own cities, but would have them all meet in the same sanctuary.

It has been said elsewhere that one altar was prescribed for them, as if God would gather them under one banner for the preservation of concord and the unity of the faith. What is added respecting the solemnity of the seventh day is very appropriate to this passage.