Have you ever wondered why God doesn't show himself in a more direct way? Why doesn't he concentrate more of his glory into a more obvious, personal message to us so that we can't help but believe? Or as many cartoons suggest, why doesn't he write a giant message in the sky "Hi! I'm God"
The answer is that he HAS revealed himself in many ways, even unto writing in the sky. Unfortunately, for each manifestation there are reasons we can't take it all in or have ignored it.
First, the theoretical concentration of God's glory is true, as much as it is possible. God has shown himself marvelously through the created universe. However, a full manifestation of God would be infinite so that we, finite beings, could not comprehend it all at once. We simply CAN'T see more of Gods glory than we do already, much less take it ALL in. We can only see one side of a mountain, much less what's beneath the surface. God can't pile more mountain around us to make us see better, we would either be squashed or still just see what's in front of us.
Job 26:14 "And these are but the outer fringe of his works; how faint the whisper we hear of him! Who then can understand the thunder of his power?”
However, consider what we ARE capable of seeing! By size alone the universe expands far beyond our current sight, stretching out across 46 billion light years in all directions and more than 4e32 cubic light years in volume. This space is filled with billions of beautiful and unique planets and gas structures, some trillions of miles high. Traveling in a straight line past these wonders at light speed would take over 9 million times the history of civilization, and this is without exploring into area or volume! As for those who are more interested in complexity and design, one only has to dip ones toes in biology or neuroscience to be amazed at the intricate, delicately balanced yet robust organic systems God has made. Poets and common people alike have wondered at the beauty of sunsets and other parts of nature. Romans 1:20 indeed holds true "For since the creation of the world God’s invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that people are without excuse."
Second, have you ever wished for a more personal and interactive message? The universe is great and massive, yet it is also cold and does not react to us. We ask, why cannot God give us something that really speaks to us. The truth is he DID. Unfortunately something interactive on our level is also constrained by our finiteness, and is subject to the passage of time. Jesus came, performed many miracles to prove that he was a message to us from God (the 'word' of God became flesh). He dies, as the epitome of that message that God is willing to die for us in his passion to love us, rises again, but then must pass.
Our only duty is remember the message, written down for us and passed down through the centuries, and learn from it.
One note here: another damper on our understanding and reception of Gods message is our refusal or preconditioning to accept the message. God's message is that he alone is great and worthy to be praised. Yes, he he loves us and has died so that we can share this glory with him, but he is still supreme, and we must conform our concept of reality to his (which is the true one). However, sin and the fall of man is the exact opposite of this. In the garden we ate of the tree of knowledge of good and evil, saying that WE had the knowledge, that WE could decide what we good and evil, not God. So we instinctively turn a blind eye to the wonderful universe God has made for us and the passionate sacrifice he made to bring us to him. Just today I read the words of Jesus talking to unbelieving Jews in John 8:43-45 "Why is my language not clear to you? Because you are unable to hear what I say. You belong to your father, the devil, and you want to carry out your father’s desires. He was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies. Yet because I tell the truth, you do not believe me!" or as 1 Corinthians 1:18 says "For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God." So it is because we love the darkness and the lies that we cannot see Gods message.
Fourth and finally, we wish for an obvious message, something we can't ignore, something clear and timeless unlike the coming of Jesus. Even though it sounds ridiculous, we might even wish for a big message written in the sky.
Well, actually, I thought about this for a little bit and I had to chuckle. If I were God, what would I write? I mean, I could write "Hi! I'm God." ... but in what language? I mean, language changes all the time and English is more of a recent phenomena. We'd only have begun to understand it in the 1700s. Perhaps God could have written it in Hieroglyphics and then Egyptian people could have passed it on to future civilizations. But how much would have been lost in wars? How could the message have developed in foklore? How much would we begin to take it for granted? How much would we explain the message as simple physical facts? By now that message in the sky would be a simple, commonly known part of nature with some ancient foklore behind it. Something like...the stars? Constellations?
Psalm 19:1 "The heavens declare the glory of God; the skies proclaim the work of his hands."
I do not hope to claim that the constellations say anything in particular. However, it would like to point out some interesting constellations. First there is the Northern Cross (most visible in the northern hemisphere around July), whose head star, one of the brightest at the time, is called Deneb "The Lord Comes".
More illustrative is the combination of Draco the Dragon, a very large constellation, whose head is directly beneath the left heel of the Hercules stars (he is standing with his feet in the north). Hercules is kneeling on his right foot because it has been wounded. This matches the prophecy back in Genesis 3:15 which refers to the coming of Jesus from the human race (though fully God). His heel will be bitten by the 'serpent' the devil as he dies on the cross, but he will crush the serpents head by conquering death. "And I will put enmity between you and the woman, and between your offspring and hers; he will crush your head, and you will strike [bruise] his heel.” Stars in the Hercules constellation have names including Ras El Gethi "The head of Him Who Bruises", Kornephorus "The Branch [i.e. of Jesse] Kneeling", and Caiam "Punishing". Near Hercules, the Christ figure, is the "Northern Crown" Corona Borealis.
Many other stars point to Christ.