The Old Testament was written by Moses and other Prophets. The Apostles and Evangelists wrote the New Testament. These men served as instruments of the Holy Spirit, who gave them His words in a spoken or written manner.
David says:
2 Sam.23:2: The Spirit of the Lord spake by me; His Word was in my tongue.
The Apostle Paul says:
Thess. 2:13: 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.
