So sad that in this day in age, we need to come up with reasons to believe God exists. This is how far our sin and wickedness has come in that we "suppress the truth". I thought the cosmological (first cause) and teleological (design) arguments were superb, but then I realized that some smart philosophers are still able to think their way around them.
At the end of the day, those who believe in God were not convinced from philosophical argumentation, but from a deep and personal sense of the presence of God. We believe because we simply do, because we cannot deny it, because we've experience him. Now all these may seem purely subjective and invalid as logical proofs, but who gives a damn? The only person who needs convincing is already convinced.
The existence of God and the Bible as God's word need nothing more than the argument: It is. Just because. It's like when your dad asks you to do something using his sheer authority and identity as his reason, "because I said so!" God started it all, not us with our tiny peanut brains. His word is the revelation of him because it is. These things should just be accepted as a matter of fact, but unfortunately we need to accommodate a world hungry for reasons and questioning everything. Proofs usually mean stating the preceding arguments that lead to a conclusion, but with God and his word, there is nothing previous to him that can be used as a reference point. He is it! The Bible said it best: In the beginning, God.