Why hasn’t God revealed Himself in an undeniable way to everybody at the same time?
Questions/charges like this take on various forms, but if it’s coming from a committed atheist, it typically sounds something like this: "If God wanted us to really know who He is, He should have...(and then they insert some personal pragmatism here). One atheist asked this question this way: God has the power to arrange the stars to read, "I AM JESUS" so everyone could see them; therefore, His existence and identity would be undeniable. So why doesn't He do that so that the maximum number of people come to know Him? Questions like this assume God is a mere pragmatist rather than The Artist of the universe, and The Author of life.
Criticizing God's design for a lack of pragmatism is like criticizing Vincent van Gogh because he added an ugly cedar tree in his Starry Night painting, or criticizing Leonardo da Vinci for the background (that is clearly unnecessary) in the Mona Lisa. I wonder if the skeptic has that much criticism for all the novelists and movie makers who don’t cut out a lot of the needless character development in the middle of the story.
Notice this also answers this rhetorical question from atheists: "Why did God design our bodies to take in food the same place we take in air (i.e. why do people die of choking from God's design)?" Once again, this question assumes mere pragmatism, and ignores the beauty of the human body. Imagine if God put our ability to eat through our elbows or armpits? How romantic could a candle-lit dinner be while two people are putting food in their elbow or their armpit?
Lastly, the more we don't understand something fully, the more we seek to understand something fully. The same way God might use pain and suffering to develop in us the virtue of compassion, God might keep himself hidden in order to grow other virtues (like faith) in us.
The bottom line is God is not a mere pragmatist. He is the wisest, holiest Artist/Author who is developing the character of those who will dwell with Him in His kingdom forever.