Your obedience, [1] etc. This is said to anticipate an objection; for he shows that he did not warn them, as though he thought unfavorably of them, but because a fall in their case was such as might have easily happened; as if he had said, -- "Your obedience is indeed commended everywhere, and for this reason I rejoice on your account: yet since it often happens, that a fall occurs through simplicity, I would have you to be harmless and simple as to the doing of evil; but in doing good, to be most prudent, whenever it may be necessary, so that you may preserve your integrity." We here see what that simplicity is which is commended in Christians; so that they have no reason to claim this distinction, who at this day count as a high virtue their stupid ignorance of the word of God. For though he approves in the Romans, that they were obedient and teachable, yet he would have them to exercise wisdom and judgment, lest their readiness to believe exposed them to impositions. So then he congratulates them, because they were free from a wicked disposition; he yet wished them to be wise, so as to exercise caution. [2]

Footnotes

1 - This he calls "faith" in Romans 1:8: so that obedience to the gospel is faith in what it declares. To believe is the special command of the gospel: hence to believe is the special act of obedience that is required; and he who believes is he who shall be saved. But this faith is that of the heart, and not of the lips; and a faith which works by love and overcomes the world, the mighty power of which we learn from Hebrew 11. -- Ed.

2 - "Good" and "evil" in this clause, is beneficence and mischief. To be wise as to good, is to be wise in acts of kindness, in promoting good, as Beza seems to take it; and to be harmless or guileless, or simple as to evil, is to exercise no arts, by plausible speeches and flatteries, as was done by those referred to in Romans 16:17, in order to do mischief, to create divisions. The Apostle's object throughout seems to have been to produce unanimity between the Jews and Gentiles. Hence in the next verse he speaks of God as "the God of peace," the author of peace among his people; and he says that this God of peace would soon tread down Satan, the author of discord, the promoter of divisions and offenses; or, as most consider the passage, he prays that God would do this; for the future, after the manner of the Hebrew, is sometimes used by the Apostle as an optative. And indeed the verb is found in some copies in this mood (suntripsai) and in the Syriac, Ethiopic, and Vulgate versions. -- Ed.

For your obedience - Romans 1:8. Your mild, obedient disposition to learn, and to obey the precepts of the teachers of religion.
I am glad - I rejoice that you evince such a disposition. But he immediately adds, that "this" was just the temper to be imposed upon, and cautions them against that danger.
Wise unto that which is good - Evince understanding of what is adapted 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 evince wisdom toward "every good" design; but to be unacquainted with "any" plan of evil. Do not yield to those plans, or follow those who would lead you into them.

For your obedience is come abroad - The apostle gives this as a reason why they should continue to hear and heed those who had led them into the path of truth, and avoid those false teachers whose doctrines tended to the subversion of their souls.
Yet I would have you wise - I would wish you carefully to discern the good from the evil, and to show your wisdom, by carefully avoiding the one and cleaving to the other.

(3) For your obedience is come abroad unto all [men]. I am glad therefore on your behalf: but yet I would have you (h) wise unto that which is good, and (i) simple concerning evil.
(3) Simplicity must be joined with wisdom.
(h) Furnished with the knowledge of the truth and wisdom, so that you may embrace good things, and avoid evil, beware of the deceits and snares of false prophets, and resist them openly: and this place plainly destroys the papists faith of credit, whereas they maintain it to be sufficient for one man to believe as another man believes, without further knowledge or examination what the matter is, or what ground it has: using these daily speeches, "We believe as our fathers believed, and we believe as the Church believes."
(i) As men that know no way to deceive, much less deceive indeed.

For your obedience is come abroad unto all men,.... That is, as the Arabic and Ethiopic versions render it, "the fame" and report of their obedience to the faith, to the doctrine of the Gospel, and the ministers of it, was spread everywhere, was well known to everyone, and spoken of with commendeth among all the churches in all nations: and this the apostle mentions as another reason why they should beware of false teachers, since it would be greatly to their reproach, should they, after all this, drop that form of doctrine which they had obeyed, desert the faithful ministers of the word, and follow these false teachers; should this be the case, they would be as notorious for their disobedience, as now for their obedience: and moreover, the apostle might hereby suggest, that whereas it was everywhere known how readily and at once they embraced the Gospel of Christ; this credulity and readiness to believe, which was their commendation, might have invited false teachers among them, who might hope and take encouragement from hence the more easily to gain upon them; and therefore they ought to be upon their watch and guard, and beware of them, and not believe every spirit:
I am glad therefore on your behalf; that they had so cheerfully and readily embraced the Gospel, and from the heart obeyed that form of doctrine delivered to them; and that their praise for this was in all the churches of Christ, and had everywhere a good report on this account:
but yet I would have you wise unto that which is good, and simple concerning evil; which is just the reverse of natural and unregenerate men, who are wise to do evil, but to do good they have no knowledge; some reference seems to be had to the words of Christ in Matthew 10:16; the apostle's meaning is, that though he rejoiced at the heartiness and simplicity of their obedience, and the credit they obtained abroad on account of it, yet was he not without his fears and jealousies concerning them; and could not but greatly wish them more wisdom to understand the doctrines of the Gospel, to discern things that differ, and approve that which is the most excellent, and hold fast that which is good; and with all their harmlessness, innocence, and simplicity, prudently guard against all evil doctrines and principles, such as might unawares lead them into bad practices, dishonourable to religion, and uncomfortable to themselves.

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 Matthew 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."

But I would have you - Not only obedient, but discreet also. Wise with regard to that which is good - As knowing in this as possible. And simple with regard to that which is evil - As ignorant of this as possible.