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.

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 it was imputed to him for righteousness. 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.

And therefore it was imputed to him for righteousness.

4:22 And therefore it was imputed to him for righteousness. The faith that secures God's righteousness is a faith that does not falter, but accepts and acts upon God's promise.

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.

Margin imputed

Or, reckoned, i.e. put to the account of. See Phile 1:18, same word:

22. And therefore it was imputed, &c.-"Let all then take notice that this was not because of anything meritorious in Abraham, but merely because he so believed."

4:13-22 The promise was made to Abraham long before the law. It points at Christ, and it refers to the promise, Ge 12:3. In Thee shall all families of the earth be blessed. The law worketh wrath, by showing that every transgressor is exposed to the Divine displeasure. As God intended to give men a title to the promised blessings, so he appointed it to be by faith, that it might be wholly of grace, to make it sure to all who were of the like precious faith with Abraham, whether Jews or Gentiles, in all ages. The justification and salvation of sinners, the taking to himself the Gentiles who had not been a people, were a gracious calling of things which are not, as though they were; and this giving a being to things that were not, proves the almighty power of God. The nature and power of Abraham's faith are shown. He believed God's testimony, and looked for the performance of his promise, firmly hoping when the case seemed hopeless. It is weakness of faith, that makes a man lie poring on the difficulties in the way of a promise. Abraham took it not for a point that would admit of argument or debate. Unbelief is at the bottom of all our staggerings at God's promises. The strength of faith appeared in its victory over fears. God honours faith; and great faith honours God. It was imputed to him for righteousness. Faith is a grace that of all others gives glory to God. Faith clearly is the instrument by which we receive the righteousness of God, the redemption which is by Christ; and that which is the instrument whereby we take or receive it, cannot be the thing itself, nor can it be the gift thereby taken and received. Abraham's faith did not justify him by its own merit or value, but as giving him a part in Christ.