John Calvin Commentary Numbers 28:16

"And in the first month, on the fourteenth day of the month, is Jehovah`s passover." — Numbers 28:16 (ASV)

And in the fourteenth day. It is true that the instruction given here has some connection with the Feast of the Passover. However, since the sacrifices are explicitly discussed, and no mention is made of its other observances except in this place, I have connected it with the continual sacrifice as its associated part.

Moses briefly refers, indeed, to what we have already seen, that is, that the people should abstain from leaven for seven days and eat unleavened bread. But he afterwards addresses the main point he intended to discuss here, namely, that the people should slay two bullocks as a burnt offering, a ram, and seven lambs, together with a goat for a sin offering, and that this sacrifice should be repeated throughout the whole week.

Therefore, so that the reverence for the Passover would be increased, this extraordinary sacrifice was added to the continual one: partly that they might thus be more and more stimulated to devote themselves to God; partly that they might acknowledge how intimately He had embraced them with His favor, since He took these offerings from their flocks and herds, and required the sacred feast to be prepared for Him from their cellars and granaries also; and partly, too, that professing themselves to be worthy of eternal death, they should turn to Him to ask for pardon and, at the same time, should understand that there was only one way of reconciliation, that is, when God would be propitiated by sacrifice.