It looks like this thread was brought back to activity in December, so I will just go ahead and and do a post.
I believe because the Bible is the only religious text that actually makes sense to me. Though I went to church some as a child, I quickly quit going and stayed away for decades. I read the bible practically zero for those decades, nor do I remember anything concrete about what I was taught as a child. Before I was a Christian, I had a broken life, and did not even know for sure if God existed. In college, I learned about different religions such as Islam, Buddhism, and Shinto. Yet, I had no interest in following any of them.
I did not read the bible nearly all of those years, until the tail end of my college years. I didn't think about religion much at all, and I was afraid to read the bible because of what could be found within its pages. Once I started reading the bible, I simply tried to read a chapter a day, starting with Matthew. I remember reading weeping and gnashing of teeth. That stuck with me, to say the least.
Anyway, over the time, I learned from the bible, and by going to different churches at the time. I did see that the bible was confusing, and I didn't fully understand it at the time (nor do I fully understand today), but the general unity was there. The explanations of why the world is the way it is made sense to me.
About the "And what has He done for you?" question, a simple spiritual answer is: Jesus Christ died for my sins, and for the sins of the whole world. He added me to his church, which is his body when I was baptized into his death. I have had my sins forgiven, and he has taken them away from me in Jesus Christ. He also forgives me of any new sins I commit when I confess them and repent of them as well. I can also take pleasure in the incredible love of God that is in Jesus Christ.
On the physical level, Jesus has given me a wife, and a sense of general peace and joy that I never had before. I have a purpose in life now, and do not feel lost or in a maze of confusion anymore. I have the gift of being able to pray to God the Father which I was not able to do before as well.
I could go on, and there is a lot of things I have left out, but that is my answer in a nutshell.
Thanks,
James