just as Abraham “believed God, and it was accounted to him for righteousness.”
def v primarily signifies to reckon, whether by calculation or imputation
The word logizomai was used as a business term, such as when a payment was given for a purchase, or putting revenues in a deposit at a storehouse.
Thus Abraham believed God, and his act of faith was placed on his account in value as righteousness. He believed God and his act of faith was credited to him for righteousness (Galatians in the Greek New Testament by Kenneth Wuest). This was neither a reward paid by God to Abraham nor did Abraham merit a payment. That would be a works-based salvation. But because Abraham cast off all dependence upon himself or anything he could do as a means of acceptance with God, and accepted God’s way of giving salvation, God answered him by giving him salvation.
Pure grace is God placing His righteousness on the believing sinners account.