19 Because that which may be known of God is manifest in them; for God hath showed it unto them.
20 For the invisible things of Him from the creation of the world are clearly seen, being understood by the things that are made, even His eternal power and Godhead; so that they are without excuse.
What this verse is saying is that man has sufficient knowledge of God from nature (creation) to be responsible to God. Man has the wisdom to draw conclusions from cause to effect.
From creation, we can grasp God’s power, His position above creation and His personality (that He is a person as opposed to an abstract principle). Psalm 19:1 — The heavens declare the glory of God; and the firmament showeth His handywork.
Manifest in them — Man is capable of knowing, so ignorance is sin.
Hath showed — the tense used refers to a completed act with continuing results.
Things that are made = literally “a poem”
Eternal power — unchangeable and omnipotent
Godhead — divinity. Man can know facts about God but can’t know God through creation alone. Knowing God comes only through Jesus Christ.
Without excuse — Man is guilty for not knowing God. An instinctive knowledge of God is built into mans’ nature so the natural man, even apart from the Law, is guilty of moral wrong.