Isn't the Bible just a book written by men?
Yes, men wrote it - and holy men of God spake as they were moved by the Holy Ghost. Here is what the Bible says of itself, what it is for, and how it invites you to test it.
Yes, the Bible was written by men. Its claim is that God spoke through them. Human authorship and divine inspiration are both part of the Bible’s own account of its origin. So the question is not who held the pen. It is whether, as Peter puts it, those men “spake as they were moved by the Holy Ghost” - and the Bible tells you what it is for, and gives you grounds to examine the claim.
What it says of itself, and what it is for
Paul, writing to a younger man who had known the Scriptures from childhood, put the origin and the purpose together:
And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, throughly furnished unto all good works.
Given by inspiration of God - and able to make you wise unto salvation through faith in Christ. That is the answer to the question behind the question: if God has spoken, what does He want you to hear? He wants you to hear how to be saved, and how to live. Peter says how the writing happened:
Knowing this first, that no prophecy of the scripture is of any private interpretation. For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.
Men spake - real men, writing. Moved by the Holy Ghost - carried by God. Paul commended a church for receiving it that way:
when ye received the word of God which ye heard of us, ye received it not as the word of men, but as it is in truth, the word of God, which effectually worketh also in you that believe.
The men were really men
God spoke through real writers, in more than one way. Luke opens his Gospel like a historian who has done his work:
It seemed good to me also, having had perfect understanding of all things from the very first, to write unto thee in order, most excellent Theophilus, That thou mightest know the certainty of those things, wherein thou hast been instructed.
Jeremiah dictated, and a scribe wrote:
Then Jeremiah called Baruch the son of Neriah: and Baruch wrote from the mouth of Jeremiah all the words of the LORD, which he had spoken unto him, upon a roll of a book.
David wept in the Psalms; Paul argued in his letters; the prophets complained to God’s face. None of that was erased. The Bible’s claim is not that God bypassed men, but that He spoke through them - and that what came out was His word.
Jesus treated it as God’s word
For a Christian, this is the decisive point. Jesus did not treat Scripture as a human book with some good ideas in it:
and the scripture cannot be broken
For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
After He rose from the dead, He showed His disciples the things written concerning Him - and what those things led to:
And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. Then opened he their understanding, that they might understand the scriptures, And said unto them, Thus it is written, and thus it behoved Christ to suffer, and to rise from the dead the third day: And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem.
Written concerning Him; fulfilled in His death and resurrection; and the result is repentance and remission of sins preached to all nations - including yours. If Jesus is who He said He is, His view of the Scriptures He held in His hands is the view to take. Who He is has its own pages on this site.
”Every religion claims its book is from God.”
Claiming divine authority does not, by itself, establish that the claim is true. That is fair, and the Bible does not pretend otherwise. It does call for trust - but it also gives testimony and a way of testing what claims to speak for God. God Himself challenges every rival to do what only He can do:
Let them bring them forth, and shew us what shall happen: let them shew the former things, what they be, that we may consider them, and know the latter end of them; or declare us things for to come. Shew the things that are to come hereafter, that we may know that ye are gods
Remember the former things of old: for I am God, and there is none else; I am God, and there is none like me, Declaring the end from the beginning, and from ancient times the things that are not yet done
And He gave His people two rules for anyone who claimed to speak in His name. A word that does not come to pass is not from Him:
When a prophet speaketh in the name of the LORD, if the thing follow not, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously
And a sign that does come to pass is still not enough, if the speaker then leads away from God:
If there arise among you a prophet, or a dreamer of dreams, and giveth thee a sign or a wonder, And the sign or the wonder come to pass, whereof he spake unto thee, saying, Let us go after other gods, which thou hast not known, and let us serve them; Thou shalt not hearken unto the words of that prophet
So the test is not only “did it happen?” but “did it happen, and did it lead to the true God?” The Bible is full of predictions made and then fulfilled, and the next page examines particular ones in their setting.
If the Bible has been used badly
Perhaps the Bible has been used against you, or you have watched religious people use it to control others. Jesus met that too, and named it. Religious leaders of His day had built a tradition that let a man withhold support from his own parents by declaring his money a gift to God:
And he said unto them, Full well ye reject the commandment of God, that ye may keep your own tradition.
Making the word of God of none effect through your tradition, which ye have delivered: and many such like things do ye.
Religious authority can be challenged by God’s own Word - Jesus did it. Those who misuse the Bible are answerable to it. Do not let the men who misused it keep you from the God who gave it.
What God is calling you toward
The Bible tells you its purpose: to make you wise unto salvation. And God tells you, in the same breath as He promises that His word will do its work, what He is inviting you to:
Seek ye the LORD while he may be found, call ye upon him while he is near: Let the wicked forsake his way, and the unrighteous man his thoughts: and let him return unto the LORD, and he will have mercy upon him; and to our God, for he will abundantly pardon.
For as the rain cometh down, and the snow from heaven, and returneth not thither, but watereth the earth, and maketh it bring forth and bud, that it may give seed to the sower, and bread to the eater: So shall my word be that goeth forth out of my mouth: it shall not return unto me void, but it shall accomplish that which I please, and it shall prosper in the thing whereto I sent it.
Abundant pardon, and a word that does not return void. You have just read a good deal of it. The next page takes up the test the Bible itself proposes - prophecy, fulfilled - and applies it to particular cases.