[Romans 4:3] As a Hebrew, a rabbi, a Sanhedrinist and a Pharisee, Paul knew exactly how to settle a Jewish argument. He could have debated the point, but instead he says, For what saith the scripture? This is a lesson we all should learn well. Whenever we are asked for a moral, ethical, or eternal answer, we should always ask ourselves, “What do the Scriptures say?" The apostle answers his own question by quoting what Moses records in Genesis 15:6. Abraham believed God, and it was counted unto him for righteousness. What do we mean when we say that faith was counted unto Abraham for righteousness? The word translated "counted" (Gr logizomai) is a commercial term which is used with regard to credits or debits. It means to set to one's credit or lay to one's charge. If you authorize your lawyer to write checks on your bank account, and he does so, although the check is written by him and money received by him, nevertheless the amount of the check is charged to you. This one word logizomai, occurs eleven times in this chapter and is translated by various words such as "count," "reckon," and "impute."

Ro 4:4-5. This principle is now further explained. Paul reasons that justification by works rests on the principle that men may earn their salvation by doing good. If this principle were true, good men would be saved by their good works and salvation would not be a gift at all. But justification by faith rests on the principle that God imputes righteousness to the ungodly as a free gift. Salvation is not, therefore, earned by the sinner but is freely given to him when he puts his faith in the blood of Jesus Christ.

Ro 4:6-8. Paul has made a case for Abraham's justification apart from works, now he strengthens that case with another Old Testament illustration. The purpose of introducing David's testimony is twofold: (1) The Jews' law regarding two witnesses (Deut 19:15; referred to by Jesus in Mt 18:16 and by Paul in II Cor 13:1 and I Tim 5:19). David corroborated what is said about Abraham and further illustrates salvation apart from works; (2) David gives witness that the same principle of justification was operative even for those living under the Mosaic law.