I was raised Presbyterian (Church of Scotland in America) and attended various youth-orientated evangelical clubs. So, I'm a Christian because, well, I was raised one.
But, I didn't really practice any religion for a long time as an adult and then in my 30's I became a Catholic. I don't really know if I know why. It just appealed to me. It all seemed so beautiful. I studied art history at university and medieval art appealed to me the most, so that was my area of focus. I was really intrigued by relics and saints and the art.
I think, growing up, I'd always been sort of confused by the idea that I was supposed to just read the Bible and pray and that would be sufficient. It wasn't sufficient. The Bible just sort of left me cold and I didn't really know how to make the connection. Then, I learned about religious art and the many ways the Catholic Church has to connect with God. There's something for everyone: liturgy, the rosary, various saints who can seem to speak to you on all sorts of levels. It was like "Oh! There are visual aids for this??"
I think, though, that what really won me over was the logic of the doctrine. I know that sounds daft to most people, but once you accept the basic premise of the Gospel, then everything flows from that in a logical sense. Like, "Since we know we are created by a loving God... then we know that XYZ is...."