36 Again, they are concerned with our original constitution, and final restoration, the types of the truth, the covenants, the first and second coming of Christ, His incarnation, sufferings and dissolution, with the resurrection, the last day, the judgment and recompense, whether sad or glorious; I, to crown all, with what we are to think of the original and blessed Trinity. Now this involves a very great risk to those who are charged with the illumination of others, if they are to avoid contracting their doctrine to a single Person, from fear of polytheism, and so leave us empty terms, if we suppose the Father and the Son and the Holy Spirit to be one and the same Person only: or, on the other hand, severing It into three, either foreign and diverse, or disordered and unprincipled, and, so to say, opposed divinities, thus falling from the opposite side into an equally dangerous error: like some distorted plant if bent far back in the opposite direction.
Source: Orations (New Advent)