Romans 1:18c

The wrath of God is being revealed from heaven against all the godlessness and wickedness of men who suppress the truth by their wickedness,

(v18, NIV)

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.

(v20, NIV)

Men are suppressing the truth. What is this truth? Looking to verse 20, Paul is talking about God's invisible qualities that have been clearly seen. The truth that is being suppressed is the truth about God. God's eternal power and divine nature are being suppressed. People don't want to face the truth about God. God is eternal and powerful, but people don't want to accept that. People love their sin too much. This is why they suppress it. They suppress it in wickedness. They suppress the truth about God in their sin because they love their sin so much. I don't need to be convinced of this, I can just look at myself. How easy and how often do I distort or disregard the truth because I am in love with sin? Look at yourself and you'll find it easy to recall situations when you've done something because of your wickedness. We are born with an allegiance to ourselves. So we often do things in opposition to God to better ourselves. I may twist the truth about lying in order to make myself feel better about lying to others. That's odd in itself: I lie to myself in order to justify lying to others. But do you want to be one of these people? These are the people whom God is revealing his wrath to. Embrace the truth and live in the truth. Do not deceive yourselves.