The Trinity refers to the Christian understanding of GOD as a unity of three persons: Father, Son, and Holy Spirit. All are equally God and so are one, each sharing in the divine attributes of ultimacy, eternity, and changelessness; yet they are distinguishable in their relations to one another and in their roles within creaturely and human life and destiny.
The doctrine of the Trinity is a postscriptural attempt to bring to coherent expression diverse affirmations about God, all of which seemed necessary to a full statement of Christian experience and belief. First, from the Hebrew Scriptures and the clear tradition of Jesus' teaching, the church affirmed that not only is God one, but God is also the creative and sovereign Father and thus, by implication, transcendent of finite limits, time, and change--all of which characterize God's creatures. Second, it was affirmed that JESUS CHRIST was more than a great prophet adopted by God; rather, he was "the Son of God," "the Word made flesh," the divine LOGOS itself incarnate in a human. Third, the HOLY SPIRIT, from whose presence the community of believers received their faith, their confidence in the truth of that faith, their holiness, and, above all, the efficacy of both baptism and the Eucharist, was necessarily also God--God's presence in their midst. For Christians, then, the one God appeared in what they called a threefold "economy," in, so to speak, three forms or modes.
Difficulties soon emerged in formulating and understanding this threefold "economy." Divergent views led early to numerous Trinitarian controversies such as those over subordinationism (the teaching that the Son is subordinate to the Father and the Holy Spirit to both; see ARIANISM) and modalism (the view that the three modes are transitory; see MONARCHIANISM and SABELLIANISM). The Councils of Nicaea (325) and Constantinople (381) outlined the dogma of the Trinity in express rejection of these teachings.
The Nicene, or Niceno-Constantinopolitan, CREED has defined through the ages, for both Catholic (Roman and Orthodox) and Reformation (Lutheran, Reformed, and Anglican) churches, the basic doctrine of the Trinity. Catholic and Protestant theology has sought in various ways to make the doctrine stated at Nicaea comprehensible. Saint Augustine's lucid analogies of the divine Trinity in our experience of ourselves as memory, understanding, and will, and in our experience of our own existence as characterized by being, truth, and love, have been the point of departure for most subsequent study. In the religious thought of the Enlightenment (17th and 18th centuries), there was a strong reaction against Trinitarianism as an "orthodox" mystery without basis in either experience or reason--this was the view of UNITARIANISM and DEISM and of much 19th-century liberal theology. The great figures of 20th-century theology--Karl BARTH, Paul TILLICH, and, most recently, Karl RAHNER--despite the ir diversity of outlook, have a gain found the Trinity a central, in fact an unavoidable, structure for expressing the Christian understanding of God.
Bibliography: Bracken, J. A., Society and Spirit (1991); Forte, B., The
Trinity as History, trans. by P. Rotondi (1991); Fortman, E. J., The
Triune God (1972); Lonergan, B. J. F., The Way to Nicaea: The
Dialectical Development of Trinitarian Theology (1976); Richardson, C.
C., The Doctrine of the Trinity (1958); Stephens, B. M., God's Last Metaphor (1981); Welch, Claude, In This Name (1952).