For your obedience is well known unto all men. I am glad therefore on your behalf: but yet I would have you wise unto that which is good, and innocent concerning evil.
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Ambrosiaster
AD 400
Being “wise as to what is good” means doing good works, while being “guileless as to what is evil” means avoiding unrighteous deeds. Commentary on Paul’s Epistles.
On account of the hearts of the innocent, the apostle, in the Epistle to the Romans, owns that he rejoices, and furnishes a kind of definition of children, so to speak, when he says, "I would have you wise toward good, but simple towards evil."