John Gill 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)

You shall also take one ram
One of the two he was bid to take, (Exodus 29:1) ;

and Aaron and his sons shall put their hands upon the head of the ram ;
confessing their sins, acknowledging their guilt, and by this act transferring the same to the ram, which was to be a burnt offering, and was typical of the imputation of sin to Christ, as before observed.