New Testament theology is what God has revealed about Himself in the New Testament. The system of New Testament theology takes the various truths that the New Testament books teach us about God and presents them in an organized fashion. The New Testament discloses the coming of the predicted Messiah in the Old Testament (Isaiah 9), the birth of the New Testament Church (the body of Christ), the Church age, the Gospel of Jesus Christ, the rejection of the Messiah by Israel, and the doctrinal beliefs applied to the believer in Jesus Christ as Savior and Lord.
The phrase “New Covenant (Testament)” was spoken by Christ at the Last Supper, and is claimed by Paul as the substance of the ministry to which he was called. He preached the Good News, the Gospel of Jesus Christ for salvation. New Testament doctrines were primarily for believers to be instructed and learn how to live lives that would be pleasing to Father God. The Old Testament deals with the record of the calling and history of the Jewish nation, and as such it is the Old Covenant. The New Testament deals with the history and application of the redemption provided by the Lord Jesus Christ on the Cross, and, as the New Covenant, it supersedes the Old.
The application of theology to the New Testament is the same as that of the Old Testament. It is the study of the progressive revelation that God gave through the New Testament writers. The study of the major doctrines of the Bible makes up a systematic theology for the believer, following the progressive revelations that God made to man from the beginning to the end of the prophetic book of Revelation. Again, theology is the gathering of facts concerning God and His Son Jesus Christ and the work of God the Holy Spirit in all the historical, present, and future events spoken of in the Bible.