Berean Study Bible
So when God wanted to make the unchanging nature of His purpose very clear to the heirs of the promise, He guaranteed it with an oath.

King James Bible
Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of his counsel, confirmed it by an oath:

American Standard Version
Wherein God, being minded to show more abundantly unto the heirs of the promise the immutability of his counsel, interposed with an oath;

Darby Bible Translation
Wherein God, willing to shew more abundantly to the heirs of the promise the unchangeableness of his purpose, intervened by an oath,

Douay-Rheims Bible
Wherein God, meaning more abundantly to shew to the heirs of the promise the immutability of his counsel, interposed an oath:

English Revised Version
Wherein God, being minded to shew more abundantly unto the heirs of the promise the immutability of his counsel, interposed with an oath:

Young's Literal Translation
in which God, more abundantly willing to shew to the heirs of the promise the immutability of his counsel, did interpose by an oath,