TSK · 2 Samuel 19:23

But Saul swore an oath to her by the LORD,“As surely as the LORD lives, you will not incur guilt in this matter!”

But the king said,“What do we have in common, you sons of Zeruiah? If he curses because the LORD has said to him,‘Curse David!’, who can say to him,‘Why have you done this?’”

If you ever do leave and cross the Kidron Valley, know for sure that you will certainly die! You will be responsible for your own death.”

For people swear by something greater than themselves, and the oath serves as a confirmation to end all dispute.