Charles Ellicott Commentary 1 Samuel 30:15

"And David said to him, Wilt thou bring me down to this troop? And he said, Swear unto me by God, that thou wilt neither kill me, nor deliver me up into the hands of my master, and I will bring thee down to this troop." — 1 Samuel 30:15 (ASV)

By God. —The oath was to be by “Elohim,” not by Jehovah, of whom the Egyptian knew nothing.

And I will bring thee down. —His accurate knowledge of the route taken by the Amalekites, and his clear account of the late raid, show that he was a person of no ordinary ability; he was probably an Egyptian merchant or wealthy trader captured in some border fray.