John Gill Commentary Leviticus 4:26

"And all the fat thereof shall he burn upon the altar, as the fat of the sacrifice of peace-offerings; and the priest shall make atonement for him as concerning his sin, and he shall be forgiven." — Leviticus 4:26 (ASV)

And he shall burn all his fat upon the altar ,
&e.] Of burnt offering, that is, the priest shall do it:

as the fat of the sacrifice of peace offerings ;
see (Leviticus 3:3–5)

and the priest shall make an atonement for him as concerning his
sin ;
in a typical way, directing to the great sacrifice of Christ, which is the only real atonement and propitiation for sin: the Vulgate Latin, Syriac, and Arabic versions, render, "the priest shall pray for him": for the pardon of his sin:

and it shall be forgiven him ;
not for the prayers of the priest, nor for the sacrifice offered up, but for the sake of Christ, the antitype of such sacrifices, and when faith was exercised on him; or the meaning is, he shall not be punished for it.