It's not the apologetics, because a lot of apologetics involves either violence to the text, such as the rather involved, complicated, and beside-the-point efforts to justify scientifcally the Deluge and a six-day creation, instead of just letting the stories be what they are; or they involve trying to convince ourselves that square pegs are round.
It's not the experience, because the experience can go be interpreted at least two ways. Do we sense God's presence during worship, or does something about the music stimulate a part of our brains that we mistake for God's presence? Those who have gone to both have remarked that attending a Grateful Dead concert is like attending a Pentecostal worship service. Those who attend churches with loud worship, heavy on guitars and drums, feel excited in the presence of God -- just as they would at a secular rock concert, because the volume triggers an adrenaline rush and makes those who listen feel excited. And those who attend somber, serious-minded services with organ worship probably feel the same sort of sober response as concert-goers listening to Bach or Mendelsohn.
It's not the transformation, because I don't see much evidence of that. I've known absolutely saintly people of just about every religion, and even with no religion, and I've known some real jerks who claim to have been born again. In fact, Frederick Douglass in his autobiography noted that the cruelest slave owners were also the most devout. Really, the Christianist sharia can be just as cruel as the Islamist one -- just ask a gay friend how much compassion you get from the church crowd if you happen to be gay; think about the way Christians so lovingly rip to shreds spouses who file for divorce; consider the paranoid thinking that often comes from our evangelical leaders about the various agendas at work to destroy all that is decent in America, and the cavalier arrogance that marks the ways we discount as foolish those whom we disagree with; recall the ways we so carelessly classify one another as "real Christians," "cultural Christians," "counterfeit Christians" and "Christians who don't get it as well as I do" based on petty stuff like baptism, eschatology, doctrines of Scriptural inspiration, ethics and sexual morals, abortion, capital punishment, and so on; and keep in mind that many Christians see nothing wrong with imposing Christian morality or views as the law of the land if we can build a large enough lobby for it. And that doesn't even touch the Christians who shoot abortionists, bomb clinics, or tacitly support those who do. When you get down to it, I see very little difference between Christians and the rest of the world as far as spiritual renewal goes. Like Voltaire said -- at least I think it was Voltaire who said it -- I'd find it easier to believe in the Savior if I knew more people who had been saved by him.
But the person of Christ is someone I can't let go of, and the Resurrection is something I just can't shake.