The necessary resistance against Arianism on the one hand, and the laborious surmounting of Sabellianism on the other, led to the development of an explicit doctrine of the Trinity. Both heresies are christological in nature. Consequently the dogma of the Trinity was evolved out of christology. It is designed to preserve faith in Christ, the Son of God, and to direct the Christian hope towards full salvation in the divine fellowship. The doctrine of the Trinity cannot therefore be termed `a speculation’. On the contrary, it is the theological premise for christology and soteriology.
Jürgen Moltmann, The Trinity and the Kingdom, p 129