I’ve heard atheists say that the best thing God could do would be to reveal Himself openly so that everyone could believe in Him, do what He wants, and not go to Hell. Since God does not do this, we know that either He does not exist or He is not good.
When this comes up with your atheist friends, try exploring the question of what would happen if God were to unequivocally prove His existence to an atheist. What would come of this? Would God’s sudden appearance change the atheist’s heart such that he would desire to devote himself to God?
Atheists aren’t idiots. An open display of powerful glory by the God of the universe would likely drive former atheists to serve Him out of fear, but what would this accomplish from God’s perspective? God doesn’t desire eternal slaves—i.e., those who work to fulfill His requirements out of a desire to escape punishment or to gain something they want. As God reminds the Israelites throughout the Old Testament, it’s not the acts of worship He’s after, but the hearts of children who adore their Father and want to be with Him.
I submit to you this illustration from The Gulag Archipelago, a book about the communist, totalitarian Soviet Union in the first half of the 20th century. This is the kind of scenario God has no interest in creating:
At the conclusion of the conference, a tribute to Comrade Stalin was called for. Of course, everyone stood up (just as everyone had leaped to his feet during the conference at every mention of his name). The small hall echoed with "stormy applause, rising to an ovation." For three minutes, four minutes, five minutes...But palms were getting sore and raised arms were already aching. And the older people were panting from exhaustion. It was becoming insufferably silly...However, who would dare be the first to stop? The secretary of the District Party Committee could have done it...But he was a newcomer. He had taken the place of a man who’d been arrested. He was afraid!...
The director of the local paper factory, an independent and strong-minded man, stood with the presidium. Aware of all the falsity and all the impossibility of the situation, he still kept on applauding! Nine minutes! Ten! In anguish he watched the secretary of the District Party Committee, but the latter dared not stop. Insanity! To the last man! With make-believe enthusiasm on their faces, looking at each other with faint hope, the district leaders were just going to go on and on applauding till they fell where they stood.
Stalin had made himself known to his people in all his power, and this was the result—forced worship given to avoid punishment. Yes, the standing ovation occurred, but it was not done out of love—it was not truthful. And for the atheist who sees God as a Stalinesque dictator, the result would be the same. This kind of "worship" does not please God; in fact, the hypocrisy of it angers Him.
A person who faults God for not openly showing His power in order to ensure that atheists will have the chance to do what they need to do to avoid Hell has missed the very purpose of God’s revelation of Himself. We exist to "glorify God and enjoy Him forever," not to grudgingly follow His orders. How would cowing the atheist into submission by His presence further this goal for the atheist? The atheist has misdiagnosed his situation: uncertainty about God’s existence is not his main problem, so certainty would not solve his problem. God is available with evidence enough to give confidence and trust to those whose hearts have been changed to desire Him. But if one hates the idea of the biblical God even in theory, one would be unlikely to love Him if He suddenly appeared in person.
The major difference between atheists and Christians is not that Christians believe God exists, but that they love Him for who He is and delight in pleasing Him, worshiping Him, and being with Him. This is why it’s a good idea to ask the atheist who blames God's lack of appearance for his unbelief, “If I were to prove without a doubt that God exists, would you then love Him?” This question gets to the heart of the real issue for the atheist.