Paul shows that with Abraham long before the Law was given, Abraham’s faith was “reckoned” to him as righteousness.
In secular Greek, the verb λογίζομαι (logizomai) was used for determining the amount of a debt (Demosthenes Or. 27, 46). The LXX uses λογίζομαι to translate חשׁב, a verb that is normally translated in as “think” or “account,” but it is used to count some action as “guilt” or “sin.” Psalm 32:2 is a good example of this: “blessed is the man against who the Lord counts no iniquity.” In Genesis 15:6 (quoted by Paul here in Romans 4:3), the word is use to say that Abraham’s faith was considered to be as righteousness. Heidland (TDNT 4:284-92) makes the point that there was nothing intrinsically good about the belief of Abraham. It is only because it pleased God that his faith was considered to be righteousness.
But all these legendary developments of Abram as a righteous man or a proto-Jew are not at all the sort of thing we read in the Hebrew Bible. There is no reason given for Abram’s call in Gen 12, nor is there any indication that Abram was a monotheist prior to his call. He was simply told that God would give him a son, and he believed that promise. God counted that belief as righteousness, even though it might not qualify as righteousness
Paul gives this word an additional theological meaning in the New Testament. Paul uses the word here and in Galatians 3:6 to described God’s declaration on the believer in Christ, making him righteous. This is the crux of salvation, moving the believer from death to life. For Paul in Romans 4, it is the faith of Abraham in Genesis 15 that “counts” as righteousness rather than his works (submitting to circumcision in Gen 17, sacrificing his son in Gen 22).
But how does this work? How is it that Paul can compare Abraham’s belief in the promise of a child to a person in the present age believing in the death of Jesus as payment for sin? Does Romans 4:22-25 say that God “imputes righteousness” to the believer on account of their faith, or does this text say that God declares the believer righteous because of the faithful act of Jesus on the cross?