19. For your obedience--that is, tractableness
      is come abroad unto all. I am glad therefore on your behalf--"I rejoice therefore over you," seems the true reading.
      but yet I would have you wise unto that which is good, and simple--"harmless," as in Mt 10:16, from which the warning is taken.
      concerning--"unto"
      evil--"Your reputation among the churches for subjection to the teaching ye have received is to me sufficient ground of confidence in you; but ye need the serpent's wisdom to discriminate between transparent truth and plausible error, with that guileless simplicity which instinctively cleaves to the one and rejects the other."

JFB.