Observe the early and general idea of sacrifices even before the giving of the law. Doth not this evidently imply that from the first, the idea was alive in the human mind of some mode of expiation. See Genesis 3:21 with Hebrews 10:5 and Revelation 13:8.
Related Commentaries of Exodus 18:12
Exodus 18:12
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.