(Read Part 1 first by clicking here.)
By the time I got to high school I was burned out of trying so hard with no measurable results, so I backed off and settled into the role of generally good teenager. This was influenced less by my spiritual convictions than by the fact that I wasn't brave enough to really rebel.
When I went to college, through different people and groups, and most notably the church I joined, I began to view my faith from a different perspective. Basically, instead of obsessing over whether I was really a Christian, I chose to believe that I was and to try to live as though I were one. I once heard Pastor Tim Keller say something that's stuck with me (he was speaking to agnostics concerned with proving the existence of God): Reasoning can get you to probability, but personal commitment will get you to certainty.
So to summarize, whereas many people, especially those who didn't grow up in the church, struggle with concepts like the virgin birth and Christ's resurrection and the reality of heaven and hell, those are things I've never questioned.
For me, the struggle has been to accept that my personal faith is genuine and that it's a gift from God, not something I can conjure with a mysterious combination of well-intended actions and carefully constructed prayers and attempts to be earnest.
The biggest thing that has helped me with that is trying (and often still failing) to choose to act in ways that demonstrate faith -- praying, reading the Bible, actively loving people, etc. -- even when I feel faithless. Experience has shown that, for me at least, feelings often follow actions. My constant challenge is to live like my faith is real, meaning it should inform and influence every aspect of my life. Of course, anyone who knows me can tell you how often I fall short of that.
That leaves out a lot of ups and downs and randomness of my journey to where I am now, but this is supposed to be a blog, not a book. If anyone has specific questions, ask away and I'll be happy to respond in comments or via email or in person.