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 recognized and treated as righteous; that is, as the friend of God. (Dr. Albert Barnes)

 

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. (Dr. Adam Clarke)

 

Not because his faith was strong, and he had a full assurance of it, but because it was right, resting on the promise of God, and relying upon his power and faithfulness to perform it; for though the righteousness of faith is not imputed to any sort of believers, not to mere nominal ones, yet to all such as have true faith, though it may be but weak; for faith, as to nature, kind, and object, though not as to degree, is the same in all true believers, and the same righteousness is imputed to one as to another. (Dr. John Gill)