The words “it was credited to him” were written not for him alone, but also for us, to whom God will credit righteousness—for us who believe in him who raised Jesus our Lord from the dead.
Paul began Romans with an analysis of man’s lost condition. The human race is under the wrath of God for its failure to receive the revelation of God that he has made in nature, and its refusal to thank God for creation and to seek him more fully in order to worship him. Instead of following the truth, people have suppressed the truth, and in its place, they have created imaginary gods like themselves and even like animals. Having turned from God, who is the source of all good, they are on a downhill path, which they will follow until they come at last to the point where they are willing to call good evil and evil good.
No one naturally agrees with this assessment, of course. It is part of what rejecting truth is all about. So Paul next spends time dealing with the arguments of those who exempt themselves from those conclusions, including the ethically moral person and the religious person. The end of his argument is that all stand condemned before God.
Finally, Paul unfolds the gospel, showing that God acted to save sinners through the Lord Jesus Christ. We cannot save ourselves. We do not deserve to be saved. But God is gracious, and because he is, he sent the Lord Jesus Christ to die in our place. By his death, Jesus turned the wrath of God aside and became the grounds on which God is able to justify the ungodly. At the end of Romans 4, Paul returns to this theme after having shown that this is the same method by which the Old Testament saints, such as Abraham, were saved and justified before God.
Abraham was saved by faith. So the question is: Do you believe in God and trust his promises, as the patriarch did? Here is what Paul says about Abraham’s faith: Abraham (1) believed God’s promise; (2) believed on the basis of the Word of God only; (3) believed in spite of adverse circumstances; (4) was fully assured that God would do whatever he had promised; and (5) acted on that confidence.
This is what the Christian faith is all about, your faith in God. That is what saves you. Hence, that is what you must do too; look to God and be saved. God promises salvation through the work of Jesus Christ. You must trust his word in this. Abraham “did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God” (Rom. 4:20). Neither should your faith falter. Receive the promise, and believe in the God who raised Jesus our Lord from the dead.
This solves the problem between God and man. As the problem is that God and man are at enmity with one another and that is why God will send those who are not his own to hell. Upon receiving the promise of God, God credits you with his righteousness which is from Christ. Consequently, this makes you to be in a right relationship with him because you are credited or clothed with a righteousness God recognizes as good. Therefore, look to God in faith (believing and trusting) and be saved.