Charles Ellicott Commentary Romans 1:19

"because that which is known of God is manifest in them; for God manifested it unto them." — Romans 1:19 (ASV)

The Apostle goes on to show how the Gentiles came to have such a knowledge of right, and how they suppressed and violated it.

They had this knowledge because they also possessed all the knowledge of God that humankind generally possessed. They knew as much as could be known without special revelation.

That which may be known.—Rather, that which is (generally and universally) known—the truths of so-called “natural religion.”

Is manifest in them.—Manifest or imprinted upon their consciences, because God had so imprinted it upon them. The marginal rendering, “to them,” is hardly tenable.