What does Romans 1:21 mean?

This section began with Paul's declaration that God's wrath is revealed against human unrighteousness. In particular, this wrath comes because God has made Himself plain enough to mankind that nobody has an excuse for ignoring Him. We may choose not to seek Him (Matthew 7:7–8), but we cannot pretend that we did not have enough evidence (Romans 1:18–20). The rest of the section will explain why that is and what God is prepared to do about it.

"Why" humanity is able to deny a God who is so obvious starts with the fact that human beings refuse to see who God is. We make a willful choice to ignore His hallmarks in the creation that surrounds us every day. In other words, we reject Him first as Creator.

Now we see that rejecting God as creator leads to a refusal to honor or give thanks to God. After all, why honor a God who did not make the world? And if God is not the creator, why would we assume that He is the provider of all we need? Why give thanks to God for what we believe we have developed and acquired for ourselves?

If we do not understand God as the creator and provider who must be worshiped, we cannot arrive at a right understanding of how the universe works. Our thinking about everything is futile, worthless from the square one. Futile thinking leads to wrong conclusions and, eventually, to darkened hearts. Everything we end up believing is based on wrong assumptions about the universe and our place in it.

For example, many will decide that a universe which God did not create and does not sustain is without meaning or purpose. That conclusion often leads to hopelessness and nihilism: the belief that life is meaningless.