1‘Now if a person sins after he hears a public adjuration to testify when he is a witness, whether he has seen or otherwise known, if he does not tell it, then he will bear his guilt. 2Or if a person touches any unclean thing, whether a carcass of an unclean beast or the carcass of unclean cattle or a carcass of unclean swarming things, though it is hidden from him and he is unclean, then he will be guilty. 3Or if he touches human uncleanness, of whatever sort his uncleanness may be with which he becomes unclean, and it is hidden from him, and then he comes to know it, he will be guilty. 4Or if a person swears thoughtlessly with his lips to do evil or to do good, in whatever matter a man may speak thoughtlessly with an oath, and it is hidden from him, and then he comes to know it, he will be guilty in one of these. 5So it shall be when he becomes guilty in one of these, that he shall confess that in which he has sinned. 6He shall also bring his guilt offering to the Lord for his sin which he has committed, a female from the flock, a lamb or a goat as a sin offering. So the priest shall make atonement on his behalf for his sin.
Verse 4 is interesting, especially in the NLT where it says something to the effect of “if you make a foolish vow…” When we promise (or vow) to do something, or be committed to something, we should not do it rashly, foolishly, or without thought. If you do this, you are in danger of being bound to do something wrong, even though it might sound like a good promise at the time. In the NLT, just the act of a foolish vow is implied to be sin, but here in the NASB we see it a little clearer, that the person is being tricked. Even though they think they are doing it for a good cause, or that their role is right and proper, the person who convinced them to swear an oath has other motives. And even unwittingly serving in an evil plot is considered sin when it is found out. We ought to be men and women of our word, so it should not be lightly that we make a promise or an oath to someone else. God wants us to be wise, not foolish, which is something that Jesus also emphasized in several parables.