Charles Ellicott Commentary Exodus 29:19

"And thou shalt take the other ram; and Aaron and his sons shall lay their hands upon the head of the ram." — Exodus 29:19 (ASV)

The other ram. —Compare to Exodus 29:1, 15. This ram is called in Leviticus (Exodus 8:22) the ram of consecration. It formed, as has been observed (Speaker’s Commentary, vol. 1 Peter 2:0, p. 535), “by far the most peculiar part of the whole ceremony.”

Consecrated to God by the act of sacrifice, its blood was used, together with the holy oil, for the consecration of Aaron and his sons (Exodus 29:20–21). At the same time, its most sacred parts were placed on their hands by Moses, so that with these they might perform their first sacerdotal act and so be inaugurated into their office (Exodus 29:22–24).

This last act was not only the crowning act of the ceremony but also its most essential feature—the act which imparted to Aaron and his sons the priestly character.