“Go, then, to all peoples everywhere and make them my disciples: baptize them in the name of the Father, the Son, and the Holy Spirit...(Matthew 28:19).
The New Testament is the major point of departure or matrix for all Trinitarian thought. This is not to deny an important role to the Old Testament, for this at the earliest stage is the mine for the great ideas which are essential for Trinitarian understanding: a personal God, rich in being, love and power; a God who acts dynamically in creating, sustaining, and redeeming the world; a God who promises the coming of a Messiah and Suffering Servant to bring in His Kingdom; and a God who relates personally to come to both the hosts of heaven and all the races of the earth. We cannot begin to comprehend a Trinitarian God apart from these theological elements. These are elements that have come naturally into the New Testament, and they have been developed as the divine promises have been fulfilled in the coming of Jesus Christ and the Holy Spirit, and as the earliest church began reflecting upon them.
Nor does the role of the New Testament deny the importance and necessity of theological exploration by systematicians who must exercise freely but judiciously their skills in finding and using ancient and also contemporary language adequate to the formulation of a doctrine of the Trinity that will make this mysterious and difficult reality relevant in each generation as history unfolds. Nevertheless, the New Testament is where all Trinitarian thought must begin formally. It is also the reference point to which all creative speculation on the Trinity must be brought back for testing and verification, and this for at least four reasons.
First, because the New Testament is chronologically the premier data bank, supplying actual Trinitarian language and simple but significant formulations, anchored as they are to a unique breakthrough in revelation at a particular point in history. Second, the New Testament provides the content of Trinitarian thought. The Gospels and Epistles identify the Persons who make up the Trinity, the particular characteristics of each, whether distinctive or overlapping, the work of each within the framework of God Himself. Third, the New Testament furnishes the major practical foci, the areas of action and application to which the Trinity is related as their source. Issues such as salvation, pastoral care, missions, healing, worship, and such. Fourth, the New Testament supplies us with more than an historical and practical source. Scripture is not merely a witness to the Word of God. It is the Word of God in its ultimate sense.