Romans 6:15

Paul’s question here is not a repetition of Romans 6:1. There he asked if we could "continue in sin" or "go on sinning." Here he said, Shall we "sin?" There he was looking at continual sinning. Here he dealt with specific acts of sin. A sinful lifestyle and acts of sin are both inappropriate for a believer who is living under God’s gracious authority.

"Surely, the objector says, we may take a night off now and then and sin a little bit ’since we are under grace.’" [Note: Robertson, 4:364.]