Romans 4:22

And therefore it was imputed to him for righteousness - The verse is thus paraphrased by Dr. Taylor: "For which reason God was graciously pleased to place his faith to his account; and to allow his fiducial reliance upon the Divine goodness, power, and faithfulness, for a title to the Divine blessing, which, otherwise, having been an idolater, he had no right to."

Abraham's strong faith in the promise of the coming Savior, for this was essential to his faith, was reckoned to him for justification: for it is not said that any righteousness, either his own, or that of another, was imputed or reckoned to him for justification; but it, i.e. his faith in God. His faith was fully persuaded of the most merciful intentions of God's goodness; and this, which, in effect, laid hold on Jesus Christ, the future Savior, was the means of his justification; being reckoned unto him in the place of personal righteousness, because it laid hold on the merit of Him who died to make an atonement for our offenses, and rose again for our justification.

And therefore - His faith was so implicit, and so unwavering, that it was a demonstration that he was the firm friend of God. He was tried, and he had such confidence in God that he showed that he was supremely attached to him, and would obey and serve him. This was reckoned as a full proof of friendship; and he was recognised and treated as righteous; that is, as the friend of God. (The true sense of faith being imputed for righteousness is given in a note at the beginning of the chapter.) See the note at Romans 4:3, 5.

4:18-21 The Apostle shows the power and excellence of that faith to which he ascribes justification. Who against hope - Against all probability, believed and hoped in the promise. The same thing is apprehended both by faith and hope; by faith, as a thing which God has spoken; by hope, as a good thing which God has promised to us. So shall thy seed be - Both natural and spiritual, as the stars of heaven for multitude. Gen 15:5.