If somebody asks me why I believe the Bible, I have a pretty straightforward answer. However it is necessary first to mention what doesn't make me believe the Bible, so that there will be no confusion when I discuss what does.
The various sciences are interesting and useful. However for almost every "find" that is supposed to prove (or disprove) the Bible a contrary view is quickly put forward.
Thus, if my faith were based on scientific discoveries, I would forever be having to keep an open mind lest some later discovery should disprove previous assumptions —a frequent event in science. I would also have to be constantly investigating the latest scientific discoveries to maintain my faith.
I have great respect for science, except of course for what is "science falsely so called" (1Timothy 6:20). However I do not regard it as a basis for belief in the Bible.
For centuries people had faith in the Bible without the modern sciences which had hardly begun to exist until a mere two centuries ago. If I believe the Bible because of science, on what basis did they believe it?
Some people believe in the Bible simply because their hearts tell them it is true. They will say, "I simply know in my heart that the Bible is truly God's word". Whilst nobody can say this sort of belief is entirely invalid, they can fairly call it a blind faith and regard it as quite unsatisfactory for themselves.
I certainly would not believe in the Bible simply because I felt it to be true. That would be far too subjective for me. No, my proof of the Bible has to be found within the Bible itself, not within my own heart and soul.
I should be able to test and examine the Bible objectively not mystically, and find it to be true or false in a reasonable manner. Otherwise my faith will be circular: "I know in my heart that the Bible is true because I know in my heart that the Bible is true." That might satisfy some people, but it does not satisfy me.
I certainly do know in my heart that the Bible is truly God's word, however the source of this knowledge is external, that is to say outside of my heart. The Bible itself says, "No one knows the thoughts of God except the Spirit of God" (1Corinthians 2:11).
It seems to me therefore, that if I claim to simply know in my own heart that the Bible is true, I am contradicting the very Bible I believe.
I once knew a four year old boy who could instantly do sums in his head. On one occasion, when asked how he got the answer, he said, "I just knowed it". But that is not how we can get the answer to the question of whether the Bible is truly God's word. We cannot just know it.
There are huge questions that only fools won't recognize. Take for example the questions we must ask about good versus evil, and the problem of death. The Bible examines those issues, and answers the questions that arise. It does so thoroughly, most reasonably, and to the complete satisfaction of anyone thirsty for answers.
As just a taste, read what Paul says about the abolition of death (1Corinthians 15:52-58), or what the letter to the Hebrews says about the solution to sin (Hebrews 7:23-28).
Unless existence is futile, and life is absurd, there must not only be answers, but also help. One of the answers about the problems inherent in evil and death, is that these problems are far too tough for us to handle by ourselves.
So we need Someone greater than we, who has formulated a plan to solve the problems, who has put that plan into effect, and who is strong enough to stop the foiling of that plan. If this has not happened, then life is a bad joke and we are victims who cannot be victors. We can only kid ourselves with platitudes like "think positive".
The Bible describes the plan and shows how it is woven into the fabric of the universe and of human history. Better still, the Bible invites us to enter into that plan, and shows us how. As just a taste, read what Paul says about the plan and purpose of God (Ephesians 1:3-14).
Many writers down through the ages have enlightened the world with jewels of truth. However you don't have to read these authors very long to also find things that are erroneous or fictitious.
If the Bible is what it claims to be, "scripture inspired by God and profitable" (2Tim 3:16) then it must not be truth mixed with error and fiction, but simply truth.
This does not mean that everyone who reads anything in the Bible will agree with it. However it does mean that anyone who will fairly allow the Bible to explain, justify, and prove itself, will find it to be consistently true through and through, "line upon line" (Isaiah 28:10), from its basic premises right through to its resulting details and conclusions.
Therefore one will let the Bible educate one's faith, mind, and conscience according to what is really true, rather than what one imagines to be true. "My thoughts are not your thoughts, nor are your ways my ways, says the Lord... a man's way is not in himself, nor is it in man who walks to direct his steps" (Isaiah 55:8, Jeremiah 10:23).