What shall we say then? Are we to continue in sin that grace may abound? (ESV)
Paul has made it very clear in the previous chapter that we are saved by grace and not by works. He has only just begun to hammer that point as he will reinforce that truth in the following chapters as well. Paul knew that his critics would have something to say about his doctrine of salvation by grace, not by works.
Who were Paul's critics? Let's consider what the Apostle Paul was before he was a believer in Jesus Christ. In Philippians 3:5–7 Paul says, "a Hebrew of Hebrews; as to the law, a Pharisee; as to zeal, a persecutor of the church; as to righteousness under the law, blameless. But whatever gain I had, I counted as loss for the sake of Christ. (ESV)"
Paul knew that his former peers, the Pharisees would view his new theology as promoting sin. In a preemptive strike against his critics Paul raises the question himself. Are we to continue in sin that grace may abound? You will likely know the answer to that question which he gives in the next verse, but it is fair to ask the question.
Does a doctrine of grace lead to holiness? Or does it lead to careless sinning? If we properly understand that we are made right with God by his work on our behalf it ought to motivate us to obey him out of a love response for his incredible gift of righteousness. On the other hand, the legalism that the Pharisees held to never saved any of them.
How do you view the doctrine of grace? Is it too risky for you? Are you trying to be "good enough" by your efforts at works? The way to holiness is not by our own effort. It is by receiving the righteousness of Christ. It is a gift. It is that simple.