What does Romans 16:19 mean?

Paul has been warning the Christians in Rome just how dangerous false teachers can be. He has urged them to be on the lookout for anyone who will teach a distorted version of Christian truth, as well as to avoid such people when they do show up. These liars are very effective, Paul insists, at deceiving those who are naive or innocent.

Now he rushes to say that the Christians in Rome have a stellar reputation for obedience to the genuine truth of the gospel. They have not been misled. By this Paul likely means that they have both trusted in Christ and have set aside sinful lifestyles. Paul rejoices that this is true of them.

Still, Paul wants them to be more than just obedient. He wants them to be wise enough to recognize false teaching when it comes their way. He wants them to know the truth so thoroughly that they immediately recognize lying distortions of it.

Paul also wants for these believers in Rome to continue to be "innocent [about] what is evil." The Greek word here is akeraios, which can also mean "unmixed, pure, or simple." He wants them to continue to avoid sinful practices instead of becoming tainted or scarred by participating in them. Jesus said something similar: "Behold, I am sending you out as sheep in the midst of wolves, so be wise as serpents and innocent as doves" (Matthew 10:16).