5. The Revelation Of God In Christ
In the sub-apostolic Church the outstanding feature is Christian experience, not theological technicality. While the doctrine of the Trinity is clearly implied, yet it is rather spiritually apprehended than intellectually expressed. Towards the end of the second century more formal language was used in the τρίας of Theophilus of Antioch and the Trinitas of Tertullian. But here again it was heresy that compelled closer definition, and the terms Person and Substance became used. Heresies as to the Person of Christ necessitated emphasis on His Deity and His distinctness from the Father, and so came substantia in Tertullian to emphasise the essential oneness with the Father. Greek writers used οὐσία and ὑπόστασις. In opposition to this came the Sabellians, who taught that the Trinity were temporary distinctions only, simple manifestations of the one Divine essence. It was this that compelled the Church to use the word “Person”. The general impression left on the reader is that the doctrine was a matter of spiritual apprehension during the first three centuries, though this became the foundation of that mental apprehension and expression which first found authoritative utterance in the Council of Nicæa. What, then, was the doctrine of Nicæa in regard to the Trinity?
1. The word “Trinity” does not occur, nor even the word “Person” in the Nicene Creed.
2. In the Creed, as then promulgated, the only reference to the Holy Spirit was “The Lord, the Life-giver”. It is clear that the Council of Nicæa desired to keep as closely as possible to the spiritual apprehension of the Trinity, but its inadequacy is seen in the way in which the doctrine is stated, partly as a spiritual reality and partly as a mental concept. Thus οὐσία is used for “substance”, though in the anathemas ὑπόστασις is found as an equivalent.
3. But this position was not tenable for long, since it was essential to show not only the relation of the Father and the Son, but also the relation of the Holy Spirit to both. While Nicæa used ὁμοούσιος in reference to the oneness of the Son to the Father, Athanasius does not employ it in regard to the Holy Spirit. But the use of terms like “substance” and “Person” led to great discussion, and the result was that πρόσωπον was disused, as implying a mere aspect and not an essential distinction. Then οὐσία became applied to the Divine Nature, and ὑπόστασις was employed to indicate the distinctions in the οὐσία. The outcome was the formula μία οὐσία ἐν τρισὶν, ὑποστάσεσιν.
4. But this made a difficulty in the West, where substantia was equivalent to essentia, and as the Latin could not possible say tres substantiæ, the terminology became fixed as una substantia, tres personæ.
5. The term “Person” is also sometimes objected to. Like all human language, it is liable to be accused of inadequacy and even positive error. It certainly must not be pressed too far, or it will lead to Tritheism. While we use the term to denote distinctions in the Godhead, we do not imply distinctions which amount to separateness, but distinctions which are associated with essential mutual co-inherence or inclusiveness. We intend by the term “Person” to express those real distinctions of Father, Son, and Holy Spirit which are found amid the oneness of the Godhead, distinctions which are no mere temporary manifestations of Deity, but essential and permanent elements within the Divine unity.
While, therefore, we are compelled to use terms like “substance” and “Person”, we are not to think of them as identical with what we understand as human substance or personality. The terms are not explanatory, but only approximately correct, as must necessarily be the case with any attempt to define the Nature of God. As already noted, it is a profound spiritual satisfaction to remember that the truth and experience of the Trinity is not dependent upon theological terminology, though it is obviously essential for us to have the most correct terms available.
 Bethune-Baker, An Introduction to the Early History of Christian Doctrine, pp. 139-147.