1.) There is good and evil in the world. We feel it, and we recognize it when we see it in ourselves and others. I believe that a higher power must exist as a differentiator between the two, and a guide to human behavior. There is an invisible standard that makes us feel something is right, wrong, good, or bad. I believe that unseen is God.
2.) I have witnessed the transformation of broken people. Myself, close friends, family, and others have moved from lives of mental illness, shame, addiction, selfishness, and immaturity to lives of kindness, health, grace, freedom, and maturity. Their eyes have turned from themselves and sought beauty and truth. They learned to love themselves and others unconditionally. They learned self-control. They found peace in incredibly painful circumstances. Over and over, I have experienced and witnessed these things.
3.). Life is full of pain and unanswerable questions. If we don't learn how to find beauty and purpose in the midst of them, it is easy to be overwhelmed. For me God was a guiding light out of the painful maze through which I was walking. Believing that there is a purpose for the pain I experience helps me to endure it with peace and patience. There are certain kinds of pain that can be numbed or avoided in life, but to keep growing, living where we are, and maturing, we must face our problems and deal with them. This means experiencing pain. Faith in the goodness, purpose, and promises of God inspires courage to face pain.
These are just a few reasons for my choice. Again, I am not looking to start a theological argument or bash anyone else's choices. Just sharing my own thoughts. :0)