Hebrews 6:18

"That by two immutable things, in which it was impossible that God should lie." What are these two? The speaking and promising; and the adding an oath to the promise. For since among men that which is confirmed by an oath is thought more worthy of credit, on this account He added that also. Seest thou that He regardeth not His own dignity, but how He may persuade men, and endures to have unworthy things said concerning Himself. That is He wishes to impart full assurance. And in the case of Abraham indeed the Apostle shows that the whole was of God, not of his patient endurance, since He was even willing to add an oath, for He by whom men swear, by Him also God "sware," that is "by Himself." They indeed as by one greater, but He not as by one greater. And yet He did it. For it is not the same thing for man to swear by himself, as for God. For man has no power over himself. Thou seest then that this is said not more for Abraham than for ourselves: "that we" (he says) "might have strong consolation, who have fled for refuge to lay hold on the hope set before us." Here too again, "after he had patiently endured he obtained the promise." "Now" he means, and he did not say "when He swore." But what the oath is, he showed, by speaking of swearing by a greater. But since the race of men is hard of belief, He condescends to the same things with ourselves. As then for our sake He swears, although it be unworthy of Him that He should not be believed, so also did the Apostle make that other statement "He learned from the things which He suffered," because men think the going through experience more worthy of reliance. What is "the hope set before us"? From these past events (he says) we conjecture the future. For if these came to pass after so long a time, so certainly the others will. So that the things which happened in regard to Abraham give us confidence also concerning the things to come.