Though he wist it not - Ignorance of the Law, or even of the consequences of the act at the time that it was committed, was not to excuse him from the obligation to offer the sacrifice.
Related Commentaries of Leviticus 5:17
Leviticus 5:17
17 And if a soul sin, and commit any of these things which are forbidden to be done by the commandments of the LORD; though he wist it not, yet is he guilty, and shall bear his iniquity.