By simple observations we deduce that everything that we see around (exist) has a cause and we know that at the beginning (whatever it place in time is) there must be an uncaused cause, the believer put God at that beginning to solve the problem of an infinite regression, but this does not means that this is the reasons why they believe and worship Him, we Christians believe in God existence by several and varied ways, the principal one is faith and that needs no proofs, we also have several solution and of noticed is God exist outside of time, in the end we realised that He exist. That He is supremely good, that He cares for us. That we can have communications with Him, this a personal and individualised experience that cannot be passed on to others, anyway I must tell you that not all believers come to believe because they need a beginning, it is not a must, what is a must is faith and we believe that this is a gift from God.