Having expressed the theme of his letter in 1:16-17 (that God gives a right standing before Him to everyone who trusts in Christ by faith), Paul begins a detailed argument from both Scripture and reason (or just plain common sense) why this MUST be so. He will begin his argument in chapters 1-3 proving that all stand equally condemned before a righteous and holy God, both Jew and Gentile alike. He begins with the Gentiles in 1:18-32.
I start by saying that the words in this short passage are some of the most frightful in all of Scripture, for they show us in glaring fashion man’s true condition before God without Christ. There are three theological presuppositions behind this passage: 1) Man is created in God’s image and thus has a faculty for knowing God implanted within by which he retains an indwelling urge to know God (John Owen, Biblical Theology, 30-31); 2) This capacity for knowing God has been horribly damaged by sin but not entirely destroyed; and, 3) God holds man accountable for his sin, and his wrath against that sin is a present reality and not something only to be experienced in a future judgment.
Paul writes, “The wrath of God is revealed from heaven against all ungodliness and unrighteousness of men.” And why is this? Because men suppress the truth. What truth? That there is a God, which God plainly shows men in His creation. The heavens declare the glory God (Psalm 19:1), and all creation shouts His name. We may add that the fact that man is created in God’s image supplies men with a conscience and a moral nature which screams the name of God within himself as well. But men don’t want to acknowledge God. It’s not that they can’t—they won’t. And it is this that darkens the mind and hardens the heart. They suppress (hold down, obstruct) the truth and do so willfully. Man prefers his sin over the truth, and so exchanges the truth for lies, lies that allow him to enjoy his sin. Man exchanges the Creator of nature for nature itself and so worships the creature instead of the Creator—which is to say he worships his sinful self and desires. And all the while, man thinks himself wise when in truth he has traded wisdom for foolishness. He will continue to sink in this condition with no way out, for he is a sinner and loves his sin, for people love darkness rather than light (John 3:19). It’s not that they won’t—they can’t.
And it is this willful imprisonment in their sin that is the expression of God’s just wrath, for being left in our sin is the greatest judgment of all.