'Took an Oath' in the Bible

And the seventh year Jehoiada sent and fetched the rulers over hundreds, with the captains and the guard, and brought them to him into the house of the LORD, and made a covenant with them, and took an oath of them in the house of the LORD, and shewed them the king's son.

Gedaliah took an oath so as to give them and their troops some assurance of safety. He said, "You don't need to be afraid to submit to the Babylonian officials. Settle down in the land and submit to the king of Babylon. Then things will go well for you."