Or if he touch the uncleanness of man, whatsoever uncleanness it be that a man shall be defiled withal, and it be hid from him; when he knoweth of it, then he shall be guilty.

Wesley's Notes

5:3 When he knoweth - As soon as he knoweth it, he must not delay to make his peace with God. Otherwise he shall be guilty - For his violation and contempt of God's authority and command.

Matthew Henry's Concise Commentary

5:1-13 The offences here noticed are, 1. A man's concealing the truth, when he was sworn as a witness to speak the truth, the whole truth, and nothing but the truth. If, in such a case, for fear of offending one that has been his friend, or may be his enemy, a man refuses to give evidence, or gives it but in part, he shall bear his iniquity. And that is a heavy burden, which, if some course be not taken to get it removed, will sink a man to hell. Let all that are called at any time to be witnesses, think of this law, and be free and open in their evidence, and take heed of prevaricating. An oath of the Lord is a sacred thing, not to be trifled with. 2. A man's touching any thing that was ceremonially unclean. Though his touching the unclean thing only made him ceremonially defiled, yet neglecting to wash himself according to the law, was either carelessness or contempt, and contracted moral guilt. As soon as God, by his Spirit, convinces our consciences of any sin or duty, we must follow the conviction, as not ashamed to own our former mistake. 3. Rash swearing, that a man will do or not do such a thing. As if the performance of his oath afterward prove unlawful, or what cannot be done. Wisdom and watchfulness beforehand would prevent these difficulties. In these cases the offender must confess his sin, and bring his offering; but the offering was not accepted, unless accompanied with confession and humble prayer for pardon. The confession must be particular; that he hath sinned in that thing. Deceit lies in generals; many will own they have sinned, for that all must own; but their sins in any one particular they are unwilling to allow. The way to be assured of pardon, and armed against sin for the future, is to confess the exact truth. If any were very poor, they might bring some flour, and that should be accepted. Thus the expense of the sin-offering was brought lower than any other, to teach that no man's poverty shall ever bar the way of his pardon. If the sinner brought two doves, one was to be offered for a sin-offering, and the other for a burnt-offering. We must first see that our peace be made with God, and then we may expect that our services for his glory will be accepted by him. To show the loathsomeness of sin, the flour, when offered, must not be made grateful to the taste by oil, or to the smell by frankincense. God, by these sacrifices, spoke comfort to those who had offended, that they might not despair, nor pine away in their sins. Likewise caution not to offend any more, remembering how expensive and troublesome it was to make atonement.