To find the answer to the very important questions of who is the author of the Bible and who wrote it (the answers to these questions are not the same), we will start from 2 Timothy 3:16 where we read:

2 Timothy 3:16 
"All Scripture is given by inspiration of God...."

The word "Scripture" in the above passage is another name for the book that today we call the Bible. What the above verse tells us is that all the Bible (“all Scripture”), was given by inspiration of God. The phrase "by inspiration of God" is actually one word in the Greek text, the word "theopneustos". This word is composed by the word "theos" that means God and the word "pneustos" that means breathed. Therefore, when the Bible says that it is "theopneustos" what it means is that it is "God-breathed", it is God’s conception, God’s idea, God’s inspiration. Hence: Author of the Bible is God who breathed it, inspired it, conceived it, authored it.

Now of course somebody may ask: "How is it that God is the author of the Bible since what I read was written by Paul, John etc.?" The Bible again gives us the answer. So, 2 Peter 1:20-21 tells us:

2 Peter 1:20-21 
"Knowing this first, that no prophecy of the Scripture is of any private interpretation, for the prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit."

Before we look closer to this passage, we must first make sure that we fully understand what "prophecy of the Scripture" means. The reason I say this is because the word prophecy is used today almost always for speaking about things of the future. However, this is not the only Biblical usage of this word. Biblically speaking, "to prophesy" means to speak things that come directly from the spiritual ground . Whether what is spoken is about the future or not is not relevant.

Having clarified what prophecy means, we can easily understand what "prophecy of the Scripture" means: it simply means the Bible as a whole, as the sum of the separate prophecies that compose it. Thus, what 2 Peter tells us is that no part of the Bible (“no prophecy of the Scripture”), came by the will of man. This means that it wasn't Paul for example, who one day decided to sit down and write a letter to Ephesians. If it happened like this, Ephesians would be written by the will of man which the Bible rules out. To find how Paul and the others made their contributions to the Bible we do not have but to continue reading in the same passage. The answer is in the latter part of verse 21 where we are told that the prophecy of the Scripture i.e. the Bible was written by holy men of God who spoke as they were moved by the Holy Spirit. Therefore, who wrote the Bible? Holy men of God. How did they write it? As they were moved by God, Who is the Holy Spirit. So yes Paul, John and the others were the writers of the Bible. But they were not the authors. The author of the Bible is God, who moved people, like Paul, Peter and John to write down what He wanted, what He authored. And if you ask how did God move them, Galatians gives us the answer for the case of Paul which is also the same for all the others:

Galatians 1:11-12
"I want you to know, brothers, that the gospel I preached is not something that man made up. I did not receive it from any man, nor was I taught it; rather I RECEIVED IT BY REVELATION..."

The way that God moved those people was not by possession, for God never possesses anybody (I Corinthians 14:32-33). Instead, it was by revelation. In other words, God told Paul what to write and Paul sat down and wrote it. Who therefore wrote Galatians? Paul. Whose ideas, signature and authorship Galatians bears? God's. Hence, who is the author? God is the author. What were men like Paul and the others that contributed to the Bible? They were the writers that wrote down what the author, God, told them. That's why the Bible, though it was written by many, has one and the same author: GOD. It is like the director and the secretary. The secretary writes down what the director tells her. Who does the writing? The secretary. Whose ideas it contains? The director's who thus is the author. And as a director can have many writers, so also God had many writers to write down what He wanted.