Charles Ellicott 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)

No harm has been done yet. Still, it is good to be on your guard.

Simple concerning evil. This is not at all the same word as the one translated “simple” above.

The first is that freedom from dishonest motives which makes a man an unsuspecting and easy prey for scheming people, and relates more to natural inclination and disposition.

The second refers more to the confirmed habit of one who has come in contact with evil and is still uncontaminated by it; who has resisted all the plots and schemes devised against him; and whose love for what is good and hatred of evil has only been strengthened and disciplined.

The word for “simple” here means “unmixed,” “uncontaminated,” “pure and clear.”