And the scripture was fulfilled which says, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God.
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Augustine of Hippo
AD 430
That Abraham believed God deep in his heart is a matter of faith alone, but that he took his son to sacrifice him . . . is not just a great act of faith but a great work as well. (Sermons 2.9)
Abraham was justified not by works but by faith. For although he had done many good things, he was not called a friend of God until he believed, and every one of his deeds was perfected by faith.
For Christ is one, in whom every nation that believes, and every tongue that confesses, is gathered unto God. And those that were of a stony heart have become the children of Abraham, the friend of God;
Abraham is the image of someone who is justified by faith alone, since what he believed was credited to him as righteousness. But he is also approved because of his works, since he offered up his son Isaac on the altar. (Gen 22:10-18) Of course he did not do this work by itself; in doing it, he remained firmly anchored in his faith, believing that through Isaac his seed would be multiplied until it was as numerous as the stars