When I was still quite a young boy, perhaps five or six, I was once alone in the front yard of our house, and I climbed to the top of the magnolia tree therein.  I stood with my feet on the last branches that would support my weight and my face uplifted into the sunshine and the breeze.  My hands were grasping twigs in order to steady myself.  My eyes were gazing into the blue. I felt a sensation of dizziness that came both from looking at the sky and from the swaying with the branches.      
I felt something else too, that which C. S. Lewis described as the sort of awe that comes from sensing the numinous.  I fancied I heard, maybe I really heard, though it seemed unlikely to me shortly after and has ever since, a voice calling to me from the sky.  All it said was my name, but it filled the earth and sky, though it was, as I thought then, above them.  I stayed there, listening, and heard it several times with a smile on my face.  Then, excited, I climbed down and ran into the house to tell the first person I found, who was, as it turned out, my Godfather, my eldest sibling, my brother, Greg.
"I was in the tree, at the very top," I told him, "and a voice called to me from the sky."
Greg was nineteen or twenty at the time.  He smiled and asked me, "What did it say?"
"It said, 'Robert, Robert."
"Oh," he said, still smiling, "Well, if it calls you again, say to it, 'Speak, Lord, your servant is listening.'"
I paused, not sure what to think of that advice, then I turned, went back out into the yard, and climbed slowly up the tree.  I reached the top and put my feet on the same branches.  My face was at the same height as before.  The sun and the breeze were the same as before.  I looked up into the sky and waited, nervous, unsure.  I did not hear anything, and I began to doubt that I had before anyway.  I was old enough to know when I was pretending, generally, but I was a little unsure.  I was sure though, that I was nervous.  I had been fine when the voice from the sky had seemed to make me important.  I was quite another thing to say to the voice that I was its servant.  
Now, I had quite thought that the voice was God's.  I had never imagined it was any other.  To be sure, Greg's advice to me was the finest advice, as good as or better than any I have ever received in any circumstance in my life.  But the simple fact was that I wanted to do what I wanted to do, and the thought of doing what someone else wanted me to do was a little off putting.  More off putting was the thought of what God might want me to do.  I knew enough Bible stories and lives of the saints to know that God asked difficult things.  I was just a boy, and I didn't really want to hear the voice again, even in pretend.  
Feeling very small, inadequate, disappointed, and willful, I climbed back down and went into the house.  I reported to Greg that I had not heard the voice again.  I believe that was when he told me the story of the calling of Samuel (1 Samuel 3), and I decided that I felt worse than before.  

This feeling of awe from sensing something numinous is a common feeling to humankind, and humankind has various ways of answering that awe.  Some say it is merely a response to things larger than ourselves.  We are awed by the size of things.  The sky, mountains, the sea, etc. are so much larger than us; what are we to do but feel smaller beside them?  That's true so far as it goes, but there is more.  There is difference between being awed by the size of things and being awed by the sense of an intelligent presence larger than one oneself, so large it is beyond the earth and the sky.  That is a different kind of largeness, a larger largeness, if you will, and a better one.  It humbled me, and I did not want to be humbled.  It was a little frightening in its awesomeness, yet I yearned for it, and the fear and yearning were at war.  
I wanted that voice.  I wanted it to call my name again, in spite of not wanting to be humble. I wasn't sure then why I wanted it.  I figured that part out later, for, whenever I had questions of the important kind, I felt the yearning for that voice. It was the voice with the answers.  How I knew, why I decided that it was the voice with the answers, I'm not sure.  Part of it, by that age, was surely because I had been told enough Bible stories to understand that Christians think God to be the truth.  But that experience with the voice, my imagination though I am confident it was, was a bit different.  
I was not pondering, as little children ponder, the mysteries of Catholicism.  I was admiring the word around me, and I was responding to an innate prompting that I think is present in all humanity.  We recognize that the universe is a made place and that it has a maker.  We see that in its order, in its beauty, in its danger even, and we see it in ourselves. We yearn for answers and instinctively recognize that the intelligence which made and ordered the universe and ourselves holds them.  I did not consciously think these things as I stood there at the top of the tree, but they were present inside me, innately.  And that was not all that was inside me at that moment, either.  Much of what I felt was, in fact, a yearning to be important.  It was arrogance and ego of a child.  Nevertheless, the sense of the numinous and the yearning for truth were also there, though I shrank from them, when I became, at my brother's prompting, aware of them.    
I have had only moments, rare ones, neither long lasting nor serious, of doubt concerning the existence of God.  I have considered the arguments against him, and found them inadequate.  I have been told by atheists that belief in a creator is foolishness, mere superstition, wishful thinking, etc... and I have considered these possibilities.  They come up short.  No theory about the origin of life or the nature of human existence adequately explains either.  At best, through the explanation of one process or another, all scientific theories can do is explain how things work and beg the questions of how they began and why they work.  It is up to philosophy and theology to explain the other questions, which, through the rigorous application of reason, they do, some quite well, others not so much.  
Science can tell us that universe is.  It cannot tell us how it became.  Observation can tell us that human beings have morality, believe in things that cannot be physically verified, have a yearning for truth, and even a need to worship. There are no biological answers to these, only analogous brain functions.  When people pray, a certain part of the brain is active, yes, but why do people pray?  And, of course, all people do not pray, yet the fact remains that it is innate in people.  The fact that experience can cause people not to pray does not negate the existence of the innate desire to worship.  The fact that some people believe there is no truth does not make them right.  In fact, the very statement, "there is no truth," is an attempt to frame the truth, albeit a failed attempt.  It is, however, a tacit admission to the existence of truth.  
We all know it deep inside, even atheists, agnostics, nihilists, and existentialists.  There is truth.  Everyone reading this knows, or knew at one time and has forgotten, that truth exists and is ascertainable to a large degree.  We have all, though we may have forgotten or since discounted it, at some point or another, stood somewhere at sometime with our faces uplifted to the sky and known.  

I believe in objective truth and in God, and certain arguments present in the works of C. S. Lewis and other authors helped me to understand why I believe.  The ones that come to mind now are the that reason alone is proof of God and the argument from desire.  Reason cannot come from unreason, hence the universe has a reasonable source, that is a mind.  Our innate desires are always toward something real, hence, we yearn for truth, because it is real.  We yearn to worship, because there is a corresponding object for our yearning.  For a more articulate and formal explanation, see the works of C. S. Lewis, such as Mere Christianity, and The Problem of Pain.  

Also see the works of Peter Kreeft, such as the link below.