Hebrews 11:18

No one could allege, that he had another son, and expected the promise to be fulfilled from him, and therefore confidently offered up this one. "And" (his words are) "he offered up his only-begotten, who had received the promises." Why sayest thou "only-begotten"? What then? Of whom was Ishmael sprung? I mean "only-begotten" (he would say) so far as relates to the word of the promise. Therefore after saying, "Only-begotten," showing that he says it for this reason, he added, "of whom it was said, In Isaac shall thy seed be called," that is, "from" him. Seest thou how he admires what was done by the Patriarch? "In Isaac shall thy seed be called," and that son he brought to be sacrificed. Afterwards, that no one may suppose he does this in despair, and in consequence of this command had cast away that Faith, but may understand that this also was truly of faith, he says that he retained that faith also, although it seem to be at variance with this. But it was not at variance. For he did not measure the power of God by human reasonings, but committed all to faith.

Great indeed was the faith of Abraham. For while in the case of Abel, and of Noah, and of Enoch, there was an opposition of reasonings only, and it was necessary to go beyond human reasonings; in this case it was necessary not only to go beyond human reasonings, but to manifest also something more. For what was of God seemed to be opposed to what was of God; and faith opposed faith, and command promise. I mean this: He had said, "Get thee out of thy country, and from thy kindred, and I will give thee this land." "He gave him none inheritance in it, no not so much as to set his foot on." Seest thou how what was done was opposed to the promise? Again He said, "In Isaac shall thy seed be called," and he believed: and again He says, Sacrifice to Me this one, who was to fill all the world from his seed. Thou seest the opposition between the commands and the promise? He enjoined things that were in contradiction to the promises, and yet not even so did the righteous man stagger, nor say he had been deceived.

He heard the opposite of the promises from Him who had made them; and yet he was not disturbed, but did them as if they had been in harmony therewith. For they were in harmony; being opposed indeed according to human calculations, but in harmony when viewed by Faith.