"It was never the intention of the original witnesses to Christ in the New Testament to set before us an intellectual problem — that of Three Divine Persons — then to tell us silently to worship this mystery of the “Three-in- One.” There is no trace of such an idea in the New Testament. This “mysterium logicum,” the fact that God is Three and yet One, lies wholly outside the message of the Bible. [This mystery has] no connection with the message of Jesus and His Apostles. No Apostle would have dreamed of thinking that there are Three Divine Persons, whose mutual relations and paradoxical unity are beyond our understanding. No “mysterium logicum,” no intellctual paradox, no antimony of Trinity in Unity, has any place in their testimony."
(Emil Brunner, Dogmatics, Vol.1, s.226)
"The first teachers of Christianity were never charged by the Jews (who unquestionably believed in the strict unity of God), with introducing any new theory of the Godhead. Many foolish and false charges were made against Christ; but this was never alleged against him or any of his disciples. When this doctrine of three persons in one God was introduced into the church, by new converts to Christianity, it caused immense excitement for many years. Referring to this, Mosheim writes, under the fourth century, “The subject of this fatal controversy, which kindled such deplorable divisions throughout the Christian world, was the doctrine of the Three Persons in the Godhead; a doctrine which in the three preceding centuries had happily escaped the vain curiosity of human researches, and had been left undefined and undetermined by any particular set of ideas.” Would there not have been some similar commotion among the Jewish people in the time of Christ, if such a view of the Godhead had been offered to their notice, and if they had been told that without belief in this they “would perish everlastingly”?"
(Frederic William Farrar, Early Days of Christianity, Vol. 1, s.55)