'Swear' in the Bible

But Jonathan had not heard that his father had required the army to swear an oath, so he stretched out the end of the staff that was in his hand and dipped it in the honeycomb. He brought it back to his mouth and his eyes brightened.

Now swear to me by the LORD that you will never eliminate my descendants after me, and that you won't erase my name from my father's family."

David asked him, "Will you take me to this raiding party?" He said, "Swear to me by God that you won't kill me or turn me over to my master, and I'll take you to the raiding party."