All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that all God's people may be thoroughly equipped for every good work. (2 Tim. 3:16-17 TNIV)
God wants to communicate with us. He gets our attention simply through the magnitude, majesty, and complexity of His Creation. We are faced with it every day. To ignore it is impossible. To explain it away is difficult...but possible. So, He gets our attention again by reversing the "natural order" of things through miracles.
Once He has our attention again, He uses the opportunity to explain some things to us. He's been revealing more details to us for over 3500 years now. Piece by piece we are able to put the picture together. We learn why things are the way they are. We know what He had in mind when He created the heavens and the earth. We know what He wants for you and for me.
The prophets heard His voice. They listened to His message. They performed miracles and made predictions. They shared His message. They wrote it down. Now we have many more details about the reality we experience every day. We have it because He designed it, He created it, He sustains it, and He explains it...in a book.