Hebrews 6:15-17

Amplified Bible, Classic Edition

¹⁵ And so it was that he [Abraham], having waited long and endured patiently, realized and obtained [in the birth of Isaac as a pledge of what was to come] what God had promised him.

¹⁶ Men indeed swear by a greater [than themselves], and with them in all disputes the oath taken for confirmation is final [ending strife].

¹⁷ Accordingly God also, in His desire to show more convincingly and beyond doubt to those who were to inherit the promise the unchangeableness of His purpose and plan, intervened (mediated) with an oath.