Let me answer your question with a somewhat tragic story.
My mom and dad were both non-practicing catholics when I was a toddler. They would go to church once in a blue moon, and were good people. Once every other blue moon, we would visit my uncle's protestant church.
One night when I was 6, my mom, dad, and I were visiting their church. We were sitting in the foyer (a room in the back that is closed off, but you can still listen to the service) because I was sick. The message that night is one you've heard before if you've spent much time at any church. Now is the time of salvation. No man is promised tomorrow. You know, things along that line.
Well, at some point in the service, my dad decided that it was time to go home. So he went to open the outer doors for us to leave, but they wouldn't open. He pushed harder, but they still wouldn't open. Finally, he had to hit the door with his shoulder, the doors opened, and we left.
He was shot and killed 2 days later.
My mom and I moved away and built a house in another town. She spent that entire summer reading the bible and asking God some tough questions. Why would a just and loving God take her husband away that she loved so much? What did that prove? Was He making her pay for some past hideous sin?
One day while she was reading, God gave her an answer (those of you who don't believe in God, this is referring to a particular scripture that seemed to "jump" out of the page and speak to her). Whatever it was, she didn't like it. She threw the bible accross the room and screamed, "THERE IS NO GOD!" She then stormed out of the house and went for a walk.
After she had cooled off, she came back home. She walked in her room and started cleaning. She saw the bible laying open and face up on the floor. She bent down to pick up. As she picked it up, her eyes fell on Psalms 14:1 "The fool says in his heart, there is no God."
It was as if the omnipotent God of the universe came into her room and pointed his finger at her and said, "Who are you to tell Me that I don't exist?"
Now, some will write all of that off as coincidence, some will see it as evidence of a higher power. But at any rate, that is why I came to believe in the bible.
And there have been many instances like that since.
Then I heard the voice of the Lord saying, "Whom shall I send? And who will go for us?" And I said, "Here am I. Send me!" Isaiah 6:8