Abram believed God, and it was reputed to him unto justice.

“Abraham, styled "the friend," [Isaiah 41:8] was found faithful, inasmuch as he rendered obedience to the words of God. He, in the exercise of obedience, went out from his own country, and from his kindred, and from his father's house, in order that, by forsaking a small territory, and a weak family, and an insignificant house, he might inherit the promises of God. For God said to him, "Get you out from your country, and from your kindred, and from your father's house, into the land which I shall show you. And I will make you a great nation, and will bless you, and make your name great, and you shall be blessed. And I will bless them that bless you, and curse them that curse you; and in you shall all the families of the earth be blessed." [Genesis 12:1-3] And again, on his departing from Lot, God said to him, "Lift up your eyes, and look from the place where you now are, northward, and southward, and eastward, and westward; for all the land which you see, to you will I give it, and to your seed forever. And I will make your seed as the dust of the earth, [so that] if a man can number the dust of the earth, then shall your seed also be numbered." [Genesis 13:14-16] And again [the Scripture] says, "God brought forth Abram, and spoke unto him, Look up now to heaven, and count the stars if you are able to number them; so shall your seed be. And Abram believed God, and it was counted to him for righteousness." [Genesis 15:5-6] On account of his faith and hospitality, a son was given him in his old age; and in the exercise of obedience, he offered him as a sacrifice to God on one of the mountains which He showed him. [Genesis 22:9]”

“Accordingly let us learn, I beseech you, a lesson for ourselves as well from the patriarch: Let us believe in the words of God and trust in his promise. Let us not apply the yardstick of our own reasoning but give evidence of deep gratitude. This, you see, will succeed in making us also be seen to be righteous and will quickly cause us to attain to the promise made by him. In Abraham's case, however, the promise was made that a complete multitude would develop from his descendants. The effect of the promise was beyond the limits of nature and human logic. Hence faith in God won righteousness for him. In our case, … if we are alert enough to see it, he promised much more. We are able in great measure to transcend human reasoning, provided we believe in the power of the One who promises, in order that we may gain also righteousness from faith and attain to the good things promised.”

“'והאמין בה AND HE BELIEVED IN THE LORD — He did not ask Him for a sign regarding this; but in respect to the promise that he would possess the land he asked for a sign, inquiring of God, במה אדע “By what sign shall I know [that I shall possess it?]” (Genesis 15:8). ויחשבה לו צדקה AND HE ACCOUNTED IT UNTO HIM FOR RIGHTEOUSNESS — The Holy One, blessed be He, accounted it unto Abraham as a merit, because of the faith with which he had trusted in Him. Another explanation of במה אדע is: he did not, by these words, ask for a sign regarding this promise that he would possess the land, but he said to Him, “Tell me by what merit they (my descendants) will remain in it (the land).” God answered him, through the merit of the sacrifices (Taanit 27b).”

“AND HE BELIEVED IN THE ETERNAL; AND HE ACCOUNTED IT TO HIM FOR RIGHTEOUSNESS. Rashi’s explanation is: The Holy One, blessed be He, accounted it to Abraham for righteousness and merit because of the faith with which he had trusted in Him. But I do not understand the nature of this merit. Why should he not believe in the G-d of truth, and he himself is the prophet, and G-d is not a man, that He should lie? Furthermore, he who believed [and on the basis of this belief was ready] to sacrifice his only son, the beloved one, and withstood the rest of the trials, how could he not believe a good tiding? The correct interpretation appears to me to be that the verse is stating that Abraham believed in G-d and he considered it due to the righteousness of the Holy One, blessed be He, that He would give him a child under all circumstances, and not because of Abram’s state of righteousness and his reward, even though He told him, Your reward shall be very great. Thus from now on he would no longer have to fear that sin might prevent the fulfillment of the promise. Now although in the case of the first prophecy Abraham had thought that the promise was conditional upon the recompense for his deeds, yet now since He promised him that he should have no fear on account of sin and that He will give him a child, he believed that the thing is established by G-d, truth He will not turn from it. For since this is a matter of the righteousness of G-d, it has no break in continuity, even as it is written, By Myself have I sworn, saith the Eternal, the word is gone forth from My mouth in righteousness, and shall not come back. It may be that the verse is stating that Abraham believed that he would have a child as an heir under all circumstances, but the Holy One, blessed be He, accounted to him that this promise He had assured him would in addition be as righteousness since in His righteousness G-d did so, just as it says, G-d thought it for good. A similar case is the verse regarding Phinehas: And that was accounted unto him for righteousness, meaning that the trust he [Phinehas] has in G-d when committing that particular deed was accounted as righteousness unto all generations since G-d will forever keep His righteousness and kindness for every generation on account of [Phinehas’ deed, and this recompense transcends any strictly merited reward]. This is similar to that which is stated, Forever will I keep for him My mercy.”

“And he believed in the Lord,.... The Targums of Onkelos and Jonathan are,"in the Word of the Lord;''in the essential Word of the Lord, in Christ the Lord his righteousness; he believed in the promise of God, that he should have a seed, and a very numerous one; he believed that the Messiah would spring from his seed; he believed in him as his Saviour and Redeemer; he believed in him for righteousness, and he believed in his righteousness as justifying him before God: and he counted it to him for righteousness; not the act of his faith, but the object of it; and not the promise he believed, but what was promised, and his faith received, even Christ and his righteousness this was imputed to him without works, and while he was an uncircumcised person, for the proof of which the apostle produces this passage, Rom 4:3; wherefore this is not to be understood of any action of his being esteemed and accounted a righteous one, and he pronounced and acknowledged a righteous person on account of it; for Abram was not justified before God by his own works, but by the righteousness of faith, as all that believe are, that is, by the righteousness of Christ revealed to faith, and received by it: what is imputed is without a man, and the imputation of it depends upon the will of another; such the righteousness of Christ without works imputed by God the Father. This is the first time we read of believing, and as early do we hear of imputed righteousness.”

“And he believed in the Lord; and he counted it to him for righteousness - This I conceive to be one of the most important passages in the whole Old Testament. It properly contains and specifies that doctrine of justification by faith which engrosses so considerable a share of the epistles of St. Paul, and at the foundation of which is the atonement made by the Son of God: And he (Abram) believed האמן heemin, he put faith) in Jehovah, ויחשבה לו vaiyachshebeita lo, and he counted it - the faith he put in Jehovah, to Him for righteousness, צדקה tsedakah, or justification; though there was no act in the case but that of the mind and heart, no work of any kind. Hence the doctrine of justification by faith, without any merit of works; for in this case there could be none - no works of Abram which could merit the salvation of the whole human race. It was the promise of God which he credited, and in the blessedness of which he became a partaker through faith. See at Gen 15:19 (note); see also on Romans 4 (note).”

“Reputed by God, who cannot judge wrong; so that Abram increased in justice by this act of faith, believing that his wife, now advanced in years, would have a child; from whom others should spring, more numerous than the stars of heaven. (Haydock) — This faith was accompanied and followed by many other acts of virtue, St. James ii. 22. (Worthington)”