John Calvin Commentary Exodus 12:14

"And this day shall be unto you for a memorial, and ye shall keep it a feast to Jehovah: throughout your generations ye shall keep it a feast by an ordinance for ever." — Exodus 12:14 (ASV)

And this day shall be to you. This is spoken of its annual celebration, which was both a monument of their exodus and a symbol of their future deliverance.

As for its being called a rite, or ordinance for ever, (edictum soeculi,) I admit that this expression means perpetuity. However, it refers only to a perpetuity that would exist until the renovation of the Church. The same explanation also applies to circumcision and the whole ceremonial of the Law.

For although by Christ’s coming the ceremonial law was abolished concerning its use, yet it only then attained its true solidity. Therefore, the difference between us and the ancient people detracts nothing from this perpetual statute. This is just as the new Covenant does not destroy the old in substance, but only in form.

A little further on, where he says, save that which every man must eat, that only may be done of you, (Exodus 12:18); the meaning is that they must cease from every work, except for preparing their day’s food. This exception is expressly made so that they may not permit themselves to violate their sacred festivals with other business.