Theophilus, second century bishop of Antioch (circa 169-183 AD), wrote an interesting defence of the Christian faith to his pagan friend Autolycus. This is a wonderful early work. Theophilus makes clear the moral and intellectual bankruptcy of Greco-Roman paganism and gives positive witness to the faith of Jesus Christ.
Below is a quote from his work where he is discussing the creation and tri-unity of the True God of Scripture:
And as the sun far surpasses the moon in power and glory, so far does God surpass man. And as the sun remains ever full, never becoming less, so does God always abide perfect, being full of all power, and understanding, and wisdom, and immortality, and all good. But the moon wanes monthly, and in a manner dies, being a type of man; then it is born again, and is crescent, for a pattern of the future resurrection. In like manner also the three days which were before the luminaries, are types of the Trinity, of God, and His Word, and His wisdom. And the fourth is the type of man, who needs light, that so there may be God, the Word, wisdom, man. Wherefore also on the fourth day the lights were made.
Christianity is, and has always been, a faith that saw in God a unity and diversity, that is a Trinity.