Charles Ellicott Commentary Leviticus 19:22

"And the priest shall make atonement for him with the ram of the trespass-offering before Jehovah for his sin which he hath sinned: and the sin which he hath sinned shall be forgiven him." — Leviticus 19:22 (ASV)

And the priest shall make an atonement. —Having offered the trespass offering according to the prescribed ritual by the priest, the sinner atoned for his sin, and was declared free by the officiating son of Aaron. (Leviticus 4:26.)