John Calvin Commentary Deuteronomy 18:3

"And this shall be the priests` due from the people, from them that offer a sacrifice, whether it be ox or sheep, that they shall give unto the priest the shoulder, and the two cheeks, and the maw." — Deuteronomy 18:3 (ASV)

And this shall be the priests’ due.

It is not only for the sake of the priests that God enumerates what He would have them receive, so that they may obtain what is their own without murmuring or dispute. He also has regard for the people, lest the priests should shamefully and greedily take more than their due.

Sacred history relates that this was done by the sons of Eli (1 Samuel 2:23), for they had advanced to such a degree of licentiousness that, like robbers, they violently seized whatever their lust desired.

Therefore, lest they should give way to this gross covetousness, God prescribes to them certain limits, to which they were to confine themselves, so that if they transgressed them, it was easy for any of the people to convict them of avarice.