John Calvin Commentary Exodus 18:12

"And Jethro, Moses` father-in-law, took a burnt-offering and sacrifices for God: and Aaron came, and all the elders of Israel, to eat bread with Moses` father-in-law before God." — Exodus 18:12 (ASV)

And Jethro. Although I do not think that Jethro had previously sacrificed to idols, yet, because he worshipped an unknown God, with only a confused and clouded faith, it appears that this was his first sincere and legitimate sacrifice since the God of Israel had been more clearly known to him.

We may gather from this that it was properly offered, because Moses, Aaron, and the elders openly professed themselves his companions and partook with him. For it is not merely said that they came to eat bread with him, but before God; this expression describes a sacred and solemn feast, a part and adjunct of the offering and divine worship.

But they never would have willingly polluted themselves with the defilements of the Gentiles to gratify an unholy man. It follows, then, that this was a sign of his piety, since they did not hesitate to become partakers with him.

We ought, indeed, to have God before our eyes as often as we partake of his bounty; but we shall later see that this expression is peculiarly applied to sacrifices, in which the faithful put themselves in the presence of God.

Yet, I do not admit that Jethro slaughtered the victims by right of the priesthood which he exercised in the land of Midian, but because there was more liberty, as will be explained in its place, before the Law was prescribed by God.

It is my decided opinion that by the word bread, the manna is unquestionably meant.