Well said, Grimpen.
Hmm. Let’s look at the doctrine, insofar as it’s possible to say anything intelligent about it in human terms.
We start by assuming that we’re operating in the Israelite/Jewish tradition: one God, distinct from and “over” (in the authority sense) His creation; anything else is superstition, misperception, fraud, temptations from demons, etc. Said God, while He does not perform epiphanies on a daily basis, does interact meaningfully with His people, does perform the occasional miracle, inspires prophets to speak in His Name. (While I grant that many an atheist, agnostic, holder of another faith tradition, etc., may not accept this as revealed truth, I’m placing it as a “given” for purposes of this explanation. You need not buy that theology as a factual assertion about the cosmos we live in, but you need to grant it as what the Jews believed about said God and cosmos.)
Now, the Jews have had a mixed history: independent nation under Judges, independent kingdoms, conquered people under Assyria (the North) and the Neobabylonians (both kingdoms), unit in the Persian Empire, part of Alexander’s short-lived Empire and first the Ptolemaic and then Seleucid monarchies that followed, independent again under the Maccabees after a revolt against the Seleucids, under the Herodians as heirs to the Maccabees, and now an part of the Roman Empire, with a couple of Herodians hanging on to pieces of it as client kings.
Into this mess comes one Yeshua, itinerant teacher and apparently miracle worker in the classic prophetic tradition. And He stands the entire Jewish doctrine on end by insisting that the entire picture is founded on a relationship of love between God and man, between man and fellow man, not the transcendent God Most High like a Shahanshah, but an immanent Abba, Father, present and loving His creation and His people, ready to forgive and lead to new and fuller life. And the consequences? He is executed as a political criminal – but in some way is known to be alive again after His death, present to His followers. Remember that sacrifices for sin, the dying god motif, and so on are present in the mindset of the greater world surrounding this event.
(Do not strain credulity looking for ways in which this can be explained in terms of modern physics, physiology, etc. – accept it as an account of their experience. If you require to believe that they were self-deluded or otherwise in error, fine, but again, take it as a “given,” a premiss of known fact from which they worked.)
Okay. The earliest Christian creed was “Jesus is Lord.” But “Lord” is a title due only to God Almighty. One early writer summarized it as, “When we see Jesus, we see God.”
Now, recall that the Greco-Roman vocabulary doesn’t draw clear lines: god/not-god, divine/sacred/secular, etc. Tiberius could call for worshiping his genius as God; Herakles is a legendary human-turned-god. And so on.
The issue here is, How can we reconcile the idea that Jesus is God, and yet prays to His Father as God, with the idea that there is only one God? And while you’re at it, what about the Paraclete, the promised Comforter, the Spirit of God which came upon the early Christians seven weeks after the Resurrection? How does that fit into the mix?
Remember that the ovum has not yet been discovered. Reproductive biology seems to indicate that when a man injects semen into a woman, she is likely to have a baby which is his child. It’s his doing that the child comes to be – they were quite familiar with ejaculations but not with the interior workings of the female reproductive system.
So… a man makes things of matter other than himself. He shapes wood into a chair, gold into jewelry, grain into bread. In contrast, in the sexual act he uses a woman to make something of the same sort as himself: his son.
If the one God is present in Jesus, who calls Him His Father, then the process is best described as begetting: God has caused another Person of the same kind as Himself, just as a man begets a son, rather than creating from that which is other than Himself, as He did in Creation. And it’s the experience of the Christians that the Holy Spirit is yet a third such Person, the promised Advocate who leads into holiness.
And yet, they must be somehow one God. Because it’s a core fact that there is only One.
Stir, mix in Platonic and Aristotelian philosophy, and allow to stew for a few decades. Result: God is one in substance: He is a single Godhead. His unity is preseerved. Yet He is equally clearly Three in terms of the Persons with whom worshippers interact: Father, Son, and Holy Spirit. And because God is eternal, so too are the three Persons eternal. The Father is ontologically prior to the others, their cause, their source. Yet all three are co-eternal.
The Eternal Son, true God, took on human form as the baby Jesus, who grew to be a man, taught, suffered, died, was buried, and rose from the dead. This was not a pious fraud, a seeming of a man: it was as truly human as any of us. Nor was the Son something that entered into Jesus somewhere along the way: God became man at the Annunciation, when Mary conceived the child that would become Immanuel, God with us in a very special way. The call to humility in Philippians 2 describes this sense in which God the Son became man best.
Truly God and truly man are not paradoxical or describing a 50:50 demigod; rather they characterize Jesus as unique. Just as an apple can at the same time be truly red and truly round, Jesus can simultaneously be truly God and truly man.
The Father sent the Holy Spirit at Jesus’s behest. But remember that ruach, pneuma, spiritus mean, indifferently, “wind, breath, spirit” – God exhaled the Holy Spirit as His Breath, His Spirit which was drawn into and envivifies His followers as the breath of life envivifies all humans. Again we have metaphor used to describe a real concept without appropriate words. In speaking of how the Holy Spirit is related to the Father, that “coming forth” (processio) is best suited to identifying how a Breath is exhaled, a Spirit sent out.
The Greek and Latin for this are useful: ousia and substantia for the One substance; hypostasis and persona for the three Persons. But in understanding that, it’s important to realize that persona was in origin the term for the mask worn by an actor to identify the character he was playing. It did not define individual autonomy but role. This led on the one hand to the heresy of modalism: that the three persons were God “playing three roles” and on the other to a tritheism of three distinct Gods; the truth is in between: three distinct Persons united in one Godhead.
Again, this does not cover all the needed discussion but serves as useful data towards grasping the idea.