So let me see if I can get the reasoning straight:
Everything that has a beginning has a cause.
The universe had a beginning.
The universe must have had a cause.
The unknown cause must be God.
The God must be a personal God.
The God must be the one described in Christianity.
The God must have inspired 66 books which are now called the Bible.
It all makes logical sense if you start with what you want to believe and work backwards. Just like JWs do with their doctrines.