Charles Ellicott Commentary Leviticus 14:19

"And the priest shall offer the sin-offering, and make atonement for him that is to be cleansed because of his uncleanness: and afterward he shall kill the burnt-offering;" — Leviticus 14:19 (ASV)

And the priest shall offer the sin offering.

The priest is now to offer the other ewe lamb, mentioned in Leviticus 14:10, as a sin offering. This offering was to expiate the sins that the restored leper had committed during his illness. During that time, he had probably expressed impatient and unbecoming sentiments concerning his loathsome condition. This sin offering was not required as a consequence of his having been in a state of uncleanness. The regulations in Leviticus 5:2-3 refer to cases when, through thoughtlessness, the unclean person forgot his duty.