John Gill 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 for him By offering his sacrifice for him, typical of the atoning sacrifice of Christ: with the ram of his trespass offering before the Lord presented before him at the door of the tabernacle, and offered up on his altar:

for his sin which he has done or "sinned", which is so expressed, according to Jarchi, to take in his sin, whether done ignorantly or presumptuously:

and the sin which he has done shall be forgiven him upon the atonement made, as all the sins of God's people are forgiven through Christ, upon the foot of his atoning sacrifice, see (Hebrews 9:22) .