For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. (ESV)
There are many people who if asked about the nature of God will give some sort of description of him being a loving deity who has no intentions of bringing any punishment to their sinful lifestyle. This kind of viewpoint is based on people's assumptions and not based on the authority of God's Word.
Paul is not ashamed of the good news of the gospel of Jesus Christ. He has made that clear in the last two verses. This verse today helps us to understand why the gospel of Jesus Christ is such good news. Jesus' sacrifice on our behalf was to take the punishment that we deserved because of our sin. Paul tells us here that God's wrath is revealed to mankind because their ungodliness.
Paul begins in this verse to tell us just how bad the situation is. We like to think that we are pretty good by nature. We use the standard of comparing ourselves to our neighbor and so we come out looking ok. The problem is that God has a much different standard. By God's standard all of us are deserving of God's wrath.
I mentioned that without a look at God's character as revealed by God's Word we come up with a false assumption about who God is. Paul tells us that it is our unrighteousness that suppresses the truth, specifically truth about God. Those that do not want to hear what the Bible says about God give evidence that their unrighteousness actively suppresses the truth.
This verse is bad news. We are all under God's wrath. The good news is that the gospel of Jesus Christ gives us a way to be forgiven as he took God's wrath on his own back on the cross. If you have not believed in Jesus Christ, stop suppressing the truth and receive his forgiveness.