Williams(i)
13 For when God made His promise to Abraham, He took an oath by Himself, since He had no one greater by whom He could take it,
14 saying: "I will certainly bless you over and over again, I will extensively increase your numbers."
15 And so by patiently waiting he obtained what God had promised him.
16 For it is a custom among men to take oath by something greater than themselves, and an oath taken for confirmation settles any dispute among them.
17 Therefore, because God wanted to make the strongest demonstration of the unchangeable character of His purpose, He interposed with an oath,