Leviticus 4:2

Ignorance. To be ignorant of what we are bound to know is sinful: and for such culpable ignorance, these sacrifices, prescribed in this and the following chapter, were appointed. (Challoner)

Not to be done. Hence the Rabbins admit sins of ignorance, only against the negative precepts. But when God forbids one thing, he commands the contrary; and we may sin by ignorance against any of his ordinances. If the ignorance be voluntary, it enhances the crime; and Aristotle well observes that drunkards, who do an injury, are to be doubly punished, because their fault is voluntary in its cause, (ad Nicom. iii. 7). But if the ignorance were perfectly involuntary, and inculpable, no sacrifice was required; so that God here speaks only of that sort of ignorance which involved some degree of negligence. This fault could not be forgiven without interior good dispositions. The sacrifice only reached to the cleansing of the flesh, (Hebrews ix. 13,) or to screen the culprit from the severity of the law and of the magistrates; (Calmet) though they might help the inward dispositions of the heart, and thus contribute to obtain God's pardon. (Origen; St. Augustine, q. 20) The difference between peccatum and delictum, is not perfectly ascertained. Some think the former word denotes sins of malice, and the latter those of ignorance. Tirinus maintains the contrary, as a more costly sacrifice, he says, is required for the latter. (Haydock)