The tension between God's keeping a secret and sharing it with others mirrors another basic dichotomy, His presence and His absence. God's presence (or His messengers') is revelatory, while His absence perpetuates the “mystery of godliness,” which the apostle Paul speaks about in I Timothy 3:16.
This same apostle pointedly tells us one of the ways God reveals Himself. Anglican clergyman J.B. Phillips captures the spirit of Paul's comments nicely:
Now the holy anger of God is disclosed from Heaven against the godlessness and evil of those men who render truth dumb and impotent by their wickedness. It is not that they do not know the truth about God; indeed he has made it quite plain to them. For since the beginning of the world the invisible attributes of God, e.g. his eternal power and deity, have been plainly discernible through things which he has made and which are commonly seen and known, thus leaving these men without a rag of excuse. They knew all the time that there is a God, yet they refused to acknowledge him as such, or to thank him for what he is or does. Thus they became fatuous in their argumentations, and plunged their silly minds still further into the dark. (Romans 1:19-21, The New Testament in Modern English)
One of the design-characteristics of God's creation is its ability to reveal the power and divinity of its Creator. It does that so clearly, Paul emphasizes, that mankind has no excuse whatsoever to deny His existence. Whether these wicked individuals instruct about astronomy in an Ivy League university's lecture hall or write a book about theology, their arguments, Paul says, are fatuous—mindless and silly.
Clouds (Part One): A Really Special Cloud
Paul is describing the perversity of human nature. That a Creator God exists is evident. Every normally intelligent person, converted or unconverted, has enough capacity to be aware of God. The natural outgrowth of this knowledge should be to glorify Him through praise and thanksgiving. The perversity appears when mankind largely ignores or resists what should be a natural inclination.
However, not everyone suppresses this tendency. Those who follow the natural inclination to praise and thank the Creator and Provider usually give their thanks to something that is not really God, but an idol. Thus, while sincere, the inclination is wrongly applied, frequently resulting in a harvest festival, as history shows.
John W. Ritenbaugh
Thanksgiving or Self-Indulgence?
"They knew God," that is, they experienced or were familiar with what He had done.
Rather than following truth, man rejects the knowledge of God. He willingly turns a blind eye to His creative powers, and instead, in his mind, replaces the faultless and perfect God with frail, perishable organisms: man, birds, reptiles, etc. He is willing to elevate almost anything above the true God.
And God allows this! In essence, He says, "If this is the way of life you choose, fine. Its consequences you bring upon yourselves!" The results are given in verses 24-25.
David C. Grabbe
What Evolution Really Means
In this passage, Paul gives a brief but appalling overview of the effect of people turning their backs on the Creator God. Mankind has worshipped the creation more than the Creator, and thus, God gave mankind over to vile affections and to a mind devoid of true judgment—his own natural mind. Since man's experiences shaped his judgment regarding conduct, his ability to judge truth became vague and led to the horrible perversions Paul lists. Today, the world groans with the weight of bearing the fruit of this idolatry.
Our own personal experience confirms the validity of these verses. Paul lists the consequences of a purely secular mind, which resulted from leaving the True Source of right standards out of our lives. He shows that when we follow the path described, we not only lose godliness but also true humanity.
John W. Ritenbaugh
The Second Commandment (1997)
They became that way! Even though God may not have given a specific calling to these people, because evidence of His existence is clearly available, God considers them to have rejected the possibility of a relationship with Him. This is how God feels about what man has done.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Eleven)
God Himself declares that at least some knowledge—a basic, foundational understanding—is available to virtually everyone. However, an interesting danger is revealed here. Note how this unfolds: ". . . because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened" (verse 21). These people knew God, just as the people addressed by Isaiah and Amos and in Hebrews had knowledge of God. Yet, they obviously did not honor God by conducting themselves according to what they knew of Him. They failed to put their knowledge into action, and instead, let their imaginations run wild and began worshipping things apart from what God had revealed of Himself. Their imaginings, Paul says, led them straight into idolatry. In other words, they did not hold fast to what God gave them.
John W. Ritenbaugh
Seeking God (Part One): Our Biggest Problem
Most of this world's holidays are based on fables, myths, and lies, while the Christian is commanded to worship God "in spirit and in truth." A true Christian does not lie and does not associate with lies, but seeks after truth in all aspects of life. If we live with a little lie now, then it is much easier to live with a worse lie later. God is emphatic on this point: A liar will not enter the Kingdom of God (Revelation 21:7-8).
Martin G. Collins
Other Forerunner Commentary entries containing Romans 1:21:
2 Thessalonians 2:3
2 Thessalonians 2:9-12
2 Timothy 2:14-17
2 Timothy 4:4
1 John 2:15-17