Romans 1:19

He proceeds to prove the principal proposition laid down in the foregoing verse; the causal particle for implies as much. Men must be justified by the righteousness of God, because they have no righteousness of their own to justify them, they themselves are all unrighteous. This he proves both of the Gentiles and Jews. He begins with the Gentiles, and proves it upon them, from this verse to Rom 2:17; and then he proves it upon the Jews also, from thence to the end of the 3rd chapter. {Rom 2:18-3:31} it is revealed in the word of God, or rather, by the judgments which he inflicteth. i.e. from God in heaven. Plagues and judgments spring not out of the dust, proceed not originally from second causes, much less do they come by chance. the abstract is put for the concrete; he means unrighteous and ungodly men; but he chooseth this way of speaking, because God, when he punisheth, aims at the sins of men; and would not punish their persons, but for their sins. By ungodliness, understand sins against the first table, which are mentioned Rom 1:21,23: by unrighteousness, sins against the second, of which there is mention at large, from Rom 1:26 to the end of the chapter. by truth, understand all that light which is left in man since the fall. There are in all men some common notions of God, his nature and will; some common principles also of equity and charity towards men, which nature itself teacheth, and upon which the consciences of the Gentiles did accuse or excuse them. These natural notions concerning God and their neighbour they did not obey and follow, but wickedly suppressed them. They imprisoned the truth which they acknowledged, that they might sin the more securely. The metaphor is taken from tyrants, who oppress the innocent, and imprison them: so the Gentiles did by the truth which they had by nature, they kept it in and under.

I. The means and helps they had to come to the knowledge of God. Though they had not such a knowledge of his law as Jacob and Israel had (Ps 147 20), yet among them he left not himself without witness (Acts 14 17): For that which may be known, etc., v. 19, 20. Observe,

That which is known of God. Or may be easily known of God, is manifest in them. The light of reason demonstrates to them the existence of one God, the maker and preserver of all things. This is made known to them from the creation of the world, or from the creatures in the world: the Creator may be discovered by the creatures, and as St. Chrysostom here says, every Scythian, every barbarian, may come to the knowledge of God by the wonderful harmony[3] of all things, which proclaims the existence of God louder than any trumpet: but having known him, they did not glorify him; they acted contrary to their knowledge, abandoning themselves to idolatry, and the vain worship of many gods, and to all manner of vices and abominations against the light of reason. (Witham)

Verses 18-25 The apostle begins to show that all mankind need the salvation of the gospel, because none could obtain the favour of God, or escape his wrath by their own works. For no man can plead that he has fulfilled all his obligations to God and to his neighbour; nor can any truly say that he has fully acted up to the light afforded him. The sinfulness of man is described as ungodliness against the laws of the first table, and unrighteousness against those of the second. The cause of that sinfulness is holding the truth in unrighteousness. All, more or less, do what they know to be wrong, and omit what they know to be right, so that the plea of ignorance cannot be allowed from any. Our Creator's invisible power and Godhead are so clearly shown in the works he has made, that even idolaters and wicked Gentiles are left without excuse. They foolishly followed idolatry; and rational creatures changed the worship of the glorious Creator, for that of brutes, reptiles, and senseless images. They wandered from God, till all traces of true religion must have been lost, had not the revelation of the gospel prevented it. For whatever may be pretended, as to the sufficiency of man's reason to discover Divine truth and moral obligation, or to govern the practice aright, facts cannot be denied. And these plainly show that men have dishonoured God by the most absurd idolatries and superstitions; and have degraded themselves by the vilest affections and most abominable deeds.