John Calvin Commentary Exodus 29:28

"and it shall be for Aaron and his sons as [their] portion for ever from the children of Israel; for it is a heave-offering: and it shall be a heave-offering from the children of Israel of the sacrifices of their peace-offerings, even their heave-offering unto Jehovah." — Exodus 29:28 (ASV)

And it shall be Aaron’s. Lest the dignity of the sacred offerings, which are called the holiness of the Lord, should be impaired, strangers are prohibited from partaking of them. For if it had been permitted that everyone should touch them and eat of them, there would have been no distinction between them and ordinary food.

Of the priests’ portion, some parts were common to all their families; but the holy parts were excepted, so that by this particular instance the reverence due to all might be instilled. The reference to place has the same purpose, for it was not lawful to eat what was holy within the walls of their houses, in order that it might be distinguished from their common and ordinary food.

For the same reason, whatever remained of it was to be burned, lest, if the flesh became spoiled, or the bread moldy, their foul odor and filthy appearance might somewhat detract from the dignity of the holy things. For the weakness of the ancient people had need of childish rudiments, which might still have a tendency to elevate the minds of the pious to things above.

This was the purpose of all these things: that no corruption should creep in which might pollute or make contemptible the service of God.