Paul paints the tragic story of man’s depravity in graphic terms and convincing logic.  One overarching point is that God is justified in condemning all.  The pagan has no excuse according to Romans 1:19-20, because “what may be known about God is plain to them, because God has made it plain to them. For since the creation of the world God’s invisible qualities – his eternal power and divine nature – have been clearly seen, being understood from what has been made, so that men are without excuse.” 

This answers the question: what happens to those who’ve never heard of Jesus Christ?  How could God judge and send them to hell?  Paul says they are without excuse, because there’s something about God everyone knows through natural revelation.

We’ve advanced significantly in science, but all we do is discover what already is. When we become overconfident with our knowledge, God often pulls the curtain back and lets us discover something more of what He has made. You can’t know all there is to know about God through natural revelation, but you can discover his eternal power and divine nature.  If you know that, even if only in part, you have reason to bow and worship, and seek to know more. Unfortunately, Paul describes man’s tragic response.  We are responsible for our response to what we know.