A minister gave a speech on this recently and it was that that made me realise why i believed it. I believe the bible is Gods word because it says it is. I believe it is the ultimate truth etc because it says it is... I also believe the old testament to be the true inspired word of God because Jesus himself often quoted from many of the books... I believ the new testament to be inspired by God because Jesus said the spirit will lead us to all truth or something like that.