Albert Barnes 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)

A burnt offering and sacrifices - This verse clearly shows that Jethro was recognized as a priest of the true God, and is of great importance in its relevance to the relation between the Israelites and their kindred peoples, and to the state of religion among the descendants of Abraham.