Faith is NOT a Work that Possesses Merit or Worth

Belief (πιστεύω) and faith (πίστις) are key words in Romans. πιστεύω (248x in NT) occurs 21x in Romans, 7x in Rom 3:21-4:25, while πίστις (244X in NT) occurs 37x in Romans, 18x in Rom 3:21-4:25.

To "believe" is to put full trust in the God who "justifies the ungodly" (Rom 4:5) by means of the gospel--the cross and resurrection of Christ. Though intellectual assent cannot be excluded from faith, the Pauline emphasis is on surrender to God as an act of the will (Rom 4:18; 10:9).

Pauline (and NT) faith is not (primarily) agreement with a set of doctrines but trust in a person. Though not explicit in Rom 1:16, another focus of Romans is the insistence that faith is in no sense a "work" (Rom 3:20, 27-28; 4:1-8; 9:31-10:8).
Therefore, although we must never go to the extreme of making the person a totally passive instrument through whom "believing" occurs -- for Paul makes clear that people are responsible to believe -- we must also insist that believing is not something we do (in the sense of "work") but is always a response, an accepting of the gift God holds out to us in his grace (see especially Rom 4:1-8). As Calvin puts it, faith is "a kind of vessel" with which we "come empty and with the mouth of our soul open to seek God's grace." (Institutes 3.11.7)

"Believing," then, while a genuinely human activity, possesses no "merit" or worth for which God is somehow bound to reward us; for salvation is, from first to last, God's work.

Reference: Douglas Moo The Epistle to the RomansNew International Commentary on the New Testament, 1996, 67-68.