Albert Barnes Commentary Romans 16:19

"For your obedience is come abroad unto all men. I rejoice therefore over you: but I would have you wise unto that which is good, and simple unto that which is evil." — Romans 16:19 (ASV)

For your obedience, etc. Romans 1:8. Your mild, obedient disposition to learn, and to obey the precepts of the teachers of religion.

I am glad, etc. I rejoice that you show such a disposition. But he immediately adds, that this was just the temperament to be deceived, and cautions them against that danger.

Wise unto that which is good. Show understanding of that which is suited to promote good and worthy ends.

Simple concerning evil. Greek, harmless. Not disposed to do wrong; having no plan, and yielding to none of the allurements of evil. You have shown your wisdom in obeying the gospel. I would have you still show wisdom towards every good design, but be unacquainted with any plan of evil. Do not yield to those plans, or follow those who would lead you into them.