Sometimes I struggle to understand the Bible, and I have questions about it, so today I've got a question that maybe you've asked too.
When people say that the Bible is "inspired" by God, what do they mean? God didn't speak out loud to the writers of the Bible and they just copied down what He said. God gave them the ideas of what He wanted them to say, and they wrote down those ideas with God's help. He made sure that they wrote everything that He wanted them to say, but they still wrote as themselves.
So the Apostle Paul has a certain way of saying things that's unique to him and that's different from how King David or Moses wrote. Here's 2 Timothy 3:16 (ERV) for some help, "All Scripture is given by God. And all Scripture is useful for teaching and for showing people what is wrong in their lives. It is useful for correcting faults and teaching the right way to live."