Question: "What is Old Testament theology?"
Answer: Old Testament theology is what God has revealed about Himself in the Old Testament. The system of Old Testament theology takes the various truths that the Old Testament books teach us about God and presents them in an organized fashion. God's revelation of Himself begins in Genesis 1:1: "In the beginning God created the heavens and the earth." That is a presupposition that all believers accept by faith and is based on the study of God throughout all the Scripture from Genesis to Revelation. Since the Bible is true in all of its aspects, then all of it, as it comes from God, is true and eternal. It never passes away nor will it ever deny itself in any of its parts.
God said, "My Word is true...it is eternal...it will never pass away." God Himself is true: Jesus said, "For I am the Way, the Truth, and the Life..." (John 14:6). John 1:1-3 state: "In the beginning was the Word, and the Word was with God, and the Word was God; the same was in the beginning with God." Paul wrote in 2 Timothy 3:16: "All Scripture is given by inspiration of God (God-breathed)." Second Peter 1:21 states: "But men spoke from God as they were carried along by the Holy Spirit."
Since God revealed Himself, His character, His attributes, etc., then a theological study is made of the Old Testament and it is discovered that the Old Testament (Old Covenant) gives us an application of theology to a relationship that God established with a created people, the Jews. We must relate the word “theology” to the word "testament" or "covenant." All through this Old Testament there is a progressive revelation of God to his people in order that they might learn who He is, what He is, and what He was doing in the world, especially with them. The application of the word “testament” carries one beyond the simple fact of books or writings to their main theme. Into the very heart of the Old Testament is woven the idea of a Covenant between God and man, first made with Adam, then with Noah, also with Abraham, the nation of Israel and with David. The Scripture refers again and again through the history, the psalms and proverbs and prophecy, to this covenant into which God entered with His chosen people. In Jeremiah, prophecy reaches its height in the sublime prediction of the New Covenant, a prediction declared by the writer of the letter to the Hebrews to be fulfilled in Jesus Christ.