This is a little background to...
The first words of the Bible are...
"In the beginning God..."
The Bible everywhere assumes the existence of God and nowhere attempts to prove it.
You do not need to prove that which is self-evident; that which everyone knows.
Read this, if you would...
"For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness; because that which may be known of God is manifest in them; for God hath shewed it unto them. For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened. Professing themselves to be wise, they became fools, and changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things."
1) God says men hold the truth (in context God is not saying men hold all truth, but the specific truth of God's existence and power).
2) The truth of God's existence is "manifest in them"--revealed, or made know, in them.
3) "God hath shewed it unto them"--God has given man this knowledge in the creation.
4) This knowledge is clearly see and understood by man.
What does man know about God without any one teaching them--intuitively? Man knows "God's eternal power and Godhead."
Eternal = God is not created. God is the non-created creator of the universe. To use philosophical terms, God is the un-caused cause.
Power = God is the all-mighty. The one that created the oceans, the sun!!! and the expansive universe with all its stars is all-powerful.
God-head = personal (thinking, reasoning, willful, feeling) Lord (ruler; king; judge) over His creation. Of course, this is not all we need to know about God, but it is the start. More on that is subsequent articles.
The first step in knowing the truth is the truth of Self-consciousness.
The second step in knowing the truth is the truth of...
Many will say, "many people are atheists" and they believe there is no God; surely, they are denying this God-consciousness.
a) Men are notorious for claiming and acting contrary to the truth. How many misguided women have gone and married a man in the face of the truth that he is a good for nothing, drunken, and a violent tempered man. "For where your treasure is, there will your heart be also." (Luke 12:34)--where you place value is where your heart will be focused / loyal / dedicated.
b) Knowing the truth and submitting our lives to the truth are two different things.
c) All cultures over all known history are God-conscious. And, by far, the vast majority of these never knew about the Bible.
Why people deny the truth about God's existence is dealt with in the Bible text above.
i) Man holds the truth in unrighteousness. He holds it but refuses to submit to it.
ii) Man knows this truth about God but decides to not glorify God in truth, nor be thankful to God for who He is and creating us, etc.
iii) The decision to believe a lie (that is what happens when you deny the truth) causes man's imaginations to become vain (worthless) and their foolish hearts to be darkened. Truth is likened unto light. If you keep blowing the candles out soon you will be groping in the dark.
iv) Man changed the glory of God into idolatry; man worships idols; man worships the creation instead of the creator--i.e. mother earth, father time, zen--getting in tune with the universe, the spirit of the bear, the fox, the water, and on we could go.
The Bible reveals, "But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him." (Hebrews 11:6) Two things: (1st) "believe that he is"--believe in the existence of God. (2nd) "that he is a rewarder of them that diligently seek him"--believe in God as your only hope.
The first point is easy. God-consciousness is what this article has been discussing. And remember I said that the Bible does not seek to prove God's existence, but assumes it because all men already know it.
The second point is what the Bible is all about. The Bible gives the TRUE answers to this. Why God is our hope? How God is our hope? Why God is our only hope? How do I enter into this hope in light of my guilt? Etc.
You ask: how do I know the Bible is true? Well, be patient, we are getting there.