Charles Ellicott Commentary Leviticus 5:4

"Or if any one swear rashly with his lips to do evil, or to do good, whatsoever it be that a man shall utter rashly with an oath, and it be hid from him; when he knoweth of it, then he shall be guilty in one of these [things]." — Leviticus 5:4 (ASV)

Pronouncing with his lips. —Better, speaking heedlessly with his lips. That is, if he uttered an oath in thoughtlessness or in passion, without his heart realising it, that he will do this or that.

To do evil, or to do good. —That is, anything whatever which is comprehended under the name good and evil, as these two categories are idiomatically used to embrace all human action. (Genesis 31:24; Numbers 24:13; Isaiah 51:23.)

Whatsoever it be that a man shall pronounce with an oath. —Better, that a man heedlessly utters with an oath. That is, anything that a man may rashly or thoughtlessly undertake to do, or to abstain from doing, with an oath.

And it be hid from him. —That is, if through this careless way in which it was done, he forgot all about it. (See Leviticus 5:2.)

When he knoweth of it ... — Better, and he then considers it, and acknowledges that he is guilty (Leviticus 4:22; Leviticus 5:2, and so on), in one of these things with regard to which a man may rashly swear that he will do or not do them, and contract guilt.