I'm not getting into a long list of the many different backgrounds of the writers, or the (often) thousands of years and of miles that separated them, or how so many of them were unaware of the others' work. All that is there for who wants to read up on it. Neither am I laying out a list of the hundreds of predictions fulfilled by the Lord Jesus during His time in the flesh. All that is true,but let's go on.
Some people ask complicated questions about how the Bible can be God's Word when the Bible says Jesus is the Word. This might be best explained by changing "word" for "revelation." From the Beginning God has been revealing Himself to mankind whether by "general revelation" like the beauty of the world around us, the many wonderful flavours available in our foods, our inner knowledge of "good" beyond any passed-down list of rules, and the nameless hunger in each of our hearts for that "something more."
Beyond all that is the "special revelation" that we call His Word. We have history of God appearing in some way to the patriarchs, kings, prophets, and even to poor shepherds. He gave each of them a message. Sometimes that message was clear and simple about something that very day, sometimes it was nothing that could have made the least bit of sense to the people at that moment, and a lot of times it was extremely embarrassing to them; but they knew God had spoken, and they did not dare edit anything out in the copies. So we know that one of Jesus' human ancestors was born from a widow seducing her father in law, that the priests in Ezekiel's day were fascinated with pornography, and that cussing somebody by his mother did not just start in the 20^th Century. We know that somebody fell asleep during Paul's preaching one night and fell off the window sill where he was sitting. And we know his name, and the fact that the fall from that upstairs window killed him, but that the Lord restored him.
It might have seemed easier to the early copyists to re-write that story to leave out the miraculous and appeal to the Greek love for wisdom and the Jewish love for scholarship, but that was how the Living God chose to reveal Himself, and that is what they would pass on.
Back on track now, God has revealed Himself through nature (including human nature), through special revelations, and through His Son. God, by His own nature, is constant, and consistent. He cannot lie, or change His mind, or get confused, so anything He says is going to fit perfectly with anything else He says. The reason we have so many "churches" today dates back to people either missing that fact or ignoring it for their own brief advantage. Brief, because the dangers of putting words in God's mouth make dancing on high-voltage wires look like fun.
So God's word is not a pile of bits and pieces to pick through, but a single "word" to you and me. If we allow His Spirit to guide us we begin to see the relationship of each part to the others so that we can even see the "sacred truths" of the various churches and teachers in light of all that God has said on the topic, putting everything in an eternal perspective.
Which things also we speak, not in the words which man's wisdom
teacheth, but which the Holy Ghost teacheth; comparing spiritual things
with spiritual. [1 Cor. 2:13]