Charles Ellicott Commentary Exodus 29:15

"Thou shalt also take the one ram; and Aaron and his sons shall lay their hands upon the head of the ram." — Exodus 29:15 (ASV)

One ram. —Hebrew, the one ram: that is, one of the two rams already mentioned in Exodus 29:1.

Put their hands upon the head of the ram.

—Again identifying themselves with the animal, as in Exodus 29:10, but with a different purpose from their former one. Then they transferred their sins to the victim; now they claimed a part in the victim’s dedication to God, offering themselves with it, and becoming, themselves, a sweet savour, an offering made by fire unto the Lord (Exodus 29:18).