But all things when they are reproved are made manifest by the light. As, for instance, when our Lord reproved the hypocrisy of the Pharisees—their practices had not seemed to the disciples very evil before, but when Christ threw on them the pure light of truth, they were made manifest in their true character—they appeared and they still appear, odious.
A just reproof places evil in a light that shows its true character. For everything which is made manifest is light. Literally, this is a truism; anything shone on is no longer dark, but light. The nearest approach to this, morally, is that light has a transforming power; when the light of the gospel shines on anything dark or evil, it transforms it into what is light or good.
This is not uniformly true; all the light of heaven turned on hell would not make it morally light; but it is the general property and tendency of moral light to transform. The exhortation would thus mean—Use your light to reprove what is evil or dark, for not only will the true character of the evil thereby be made apparent, but your light will have a transforming power.
But if this were the meaning, we should expect in the end of the verse, not φῶς ἐστι, but φῶς γινεταί, to denote this transformation. The rendering of A.V., giving to φανερούμενον an active meaning ("whatsoever doth make manifest is light"), is rejected by most grammarians, as not being consistent with the usage of the word.
The meaning which that rendering gives is this: "Light is the element which makes all clear." We should thus have in the latter clause a proposition, affirming as universal what in the former clause is affirmed of one particular case; "things reproved are made manifest by the light, for it is only light that makes things clear."
The exhortation to reprove would thus be confirmed by the consideration that the only way of making immoral things appear in their proper character is to let in on them the light of the gospel. The great practical point is that Christians ought to let in and diffuse the light.