Hebrews 6 17
That's why God wanted to demonstrate more clearly to those who would inherit the promise that he would never ever change his mind.
Compare with other 3 random translations
ASV Hebrews 6:17Wherein God, being minded to show more abundantly unto the heirs of the promise the immutability of his counsel, interposed with an oath;
ERV Hebrews 6:17God wanted to prove that his promise was true. He wanted to prove this to those who would get what he promised. He wanted them to understand clearly that his purposes never change. So God said something would happen, and he proved what he said by adding an oath.
AMP Hebrews 6:17In the same way God, in His desire to show to the heirs of the promise the unchangeable nature of His purpose, intervened and guaranteed it with an oath,