But all things that are reproved - Dr. Macknight paraphrases this verse as follows: "Now all these reprovable actions, ελεγχομενα, which are practised in celebrating these mysteries, are made manifest as sinful by the Gospel; and, seeing every thing which discovers the true nature of actions is light, the Gospel, which discovers the evil nature of the actions performed in these mysteries, is light."
The apostle speaks against these mysteries as he speaks against fornication, uncleanness, and covetousness; but by no means either borrows expression or similitude from them to illustrate Divine truths; for, as it would be a shame even to speak of those things, surely it would be an abomination to allude to them in the illustration of the doctrines of the Gospel.
But all things that are reproved - Margin, discovered. The word used here properly means proved, demonstrated, reproved, or convicted (see the notes on John 16:8); but it seems here to be used in the sense of disclosed, or discovered. The sense is, that “its true nature is demonstrated;” that is, it is made known.
Are made manifest by the light - The sense is, “light is the means of seeing what things are. We discern their form, nature, appearance, by it. So it is with the gospel - the light of the world. It enables us to see the true nature of actions. They are done in darkness, and are like objects in the dark. Their form and nature cannot then be known; but, when the light shines, we see what they are;” compare notes on John 3:20-21.
For whatsoever doth make manifest is light - “Anything which will show the real form and nature of an object, deserves to be called light.” Of the truth of this, no one can doubt. The meaning in this connection is, that that system which discloses the true nature of what is done by the pagan, deserves to be considered as “light;” and that the gospel which does this, should be regarded as a system of light and truth. It discloses their odiousness and vileness, and it stands thus in strong contrast with all the false and abominable systems which have upheld or produced those vices.