The great themes of repentance and conversion were part of the apostolic preaching from the beginning (Acts 2:38; 3:26). Paul taught clearly that good works could save no one (Rom. 3:28). But he also taught that consequent good works were a necessity to demonstrate the genuineness of the conversion (Eph. 2:8-10). By grace a person must change the way he thinks and lives, must turn his life around from sin and selfishness to God, and must so live that people can see the seriousness of his choice for Christ. Only the transforming power of Christ can work such a change.
—Stewart Custer, Witness to Christ: A Commentary on Acts, 366