I don't see the separation. God the Son, God the Father, and God the Holy Spirit are the three aspects of the Triune Christian God. That doesn't mean that they're in any way separate from each other.
Uh, just exactly when did Christianity reach Ireland, so that they could become acquainted with the Shamrock? The classic physical metaphor for the Trinity (from Eric Idle's
Nuns on the Run, "In the name of The Father, and the Son, and the Holy Shamrock"; though the testimony of others has supported the Shamrock as being used to exemplify the Trinity).
By the time we got to the Council of Nicea which defined precisely what Christianity was, about three centuries after the fact, there were many interpretations and many gospels and other religious texts. But it was only the
officially recognized interpretations and texts that were selected and allowed to survive, as the others were destroyed. Trinitarianism was not the norm, but rather the doctrine that was selected arbitrarily by the Council. Unitarianism also existed and was resurrected a few times thereafter.