In this passage, Paul explains why people need the righteousness revealed in the gospel – because God’s wrath is revealed from heaven against their unrighteousness and ungodliness. He begins by saying that God’s wrath, or hateful anger, is revealed in the present against the evil of man. This evil manifests itself in two ways: ungodliness and unrighteousness. Ungodliness is the characteristic of natural humans to be unlike God. In other words, although they were originally made to reflect God’s character, they fail to do so. For example, because God is love and truth, people ought to be loving and truthful. However, because they are ungodly, they are not. Unrighteousness refers to the failure of people to obey God’s law, which is revealed by their consciences and His Word. Paul says that, by men’s disobedience of God, they suppress the truth about Him.
In verse 19, Paul begins to explain why it is possible that people can suppress the truth about God, rather than be ignorant of Him. The first reason is because God has given the truth about Him to their minds. In verse 20, he explains that God has done this by revealing who He is through creation. Therefore, they are not ignorant of Him, and have no excuse for their suppression of the truth about Him.
In verse 21, Paul explains how men suppressed the truth about God. They did so by failing to honor Him, or give thanks to Him, but speculated about lies contrary to the truth about Him, and had their hearts made worse by their speculations. Therefore, Paul says in verse 23, they made gods out of men and animals.
In verse 24, Paul explains God’s wrathful response to their idolatry. The response was to give them further opportunity to become more idolatrous. Thus, according to verse 25, they fully replaced the truth about God with a lie, and worshiped and served creatures.
In verse 26, Paul introduces what God’s wrathful response was to their complete idolatry. The response was to give them the freedom to be enslaved by their sexual perversion. Therefore, homosexuality was invented by them. In verse 27, Paul explains that the result of homosexuality was that the male homosexuals were physically harmed by practicing homosexuality.
In verse 28, Paul gives God’s final wrathful response to unrighteousness. As they had reached the point in which they practiced homosexuality, they did not acknowledge God at all. Therefore, God let them be enslaved by depraved minds, so that they became full of all unrighteousness and ungodliness, which is the point at which they are now.