Here belief and trust have brought about an obedient response to the divine gift of Jesus and the decrees that, when obeyed from the heart, bring one into that state of "freedom from sin" made accessible in the act of baptism (6:3-11). From that day forward, the person who has thus responded in faith must continue to act in faith by being a "servant of righteousness."
Sounds like it's the concept of "from faith to faith" that Paul talks about in Rom 1.16-17.