The Trinity is Christianity’s most criticized doctrine, partly because it is so misunderstood by those unaware of its beauty. In fact, most of the criticism only parodies it and attacks its distortions. To understand it truly, we must consider 1) what the doctrine is, 2) what it does, 3) where it came from, and 4) why it matters.
First, contrary to much criticism, the doctrine of the Trinity is logical. It doesn’t say God is simultaneously one God and three gods, or one person and three persons. Rather, it says he has always been only one God, with neither rival nor peer. But he is three eternal persons—Father, Son and Holy Spirit—in one being. The terms Father and Son simply point to the love, intimacy and trust between the persons of the Trinity, analogous to the relationship between a father and son. The words emphatically do not mean God had sex with Mary, who remained a virgin in Jesus’ conception.
Second, the doctrine helps us understand God’s greatness, but just to a point since mere mortals can’t fully comprehend his being. Because our experience tells us persons are always separate entities, we naturally rebel against a doctrine that transcends our categories. But to reject the Trinity on that basis would be like a worm’s insisting that humans can’t possibly be as complex as we are in fact. The doctrine of the Trinity, then, marks off a sacred space in which we can approach God’s exalted majesty, as one being—and only one—yet with three distinct persons. We must not limit him to the flat oneness we see around us. Nor can we refuse to allow that he could transcend his own categories to become human. For by so doing, we reduce him to the level of a created being and so dishonor him. By contrast, this doctrine opens us to all that God has revealed of himself and enables us to worship him truly, in all his fullness.
Third, while Jesus’ apostles never used the term Trinity, they definitely believed the truths it brings together—e.g. that in worshipping Jesus and the Holy Spirit, they worshipped the one true God. God’s revelation of himself transcended the apostles’ categories, yet they remained faithful to his revelation, even though they had no word for it. Centuries later Church leaders offered the term “Trinity” as the best descriptor of God's tri-unity. So the term represents a case of theological catch-up. Its lateness doesn't imply that the doctrine was a human invention, a late add-on. Rather, it suggests the opposite—that the concept of the Trinity wasn’t human in origin, but divine. (Some may wonder why the Jewish scriptures don’t clearly teach the Trinity. They do hint at it: Psalm 110, for example, refers to the Messiah in God-like terms and Isaiah 61:1 speaks of God's anointing the Messiah with his Spirit. The reason they don’t do more is that there simply was no need to understand God’s plurality-in-unity before Jesus came.)
Last, some reject the Trinity, as a pointless theological complication. Truly understood, however, God’s plurality is no less vital than his unity. Lacking a plurality of persons, he couldn’t be both genuinely loving and self-sufficient because he would have had to create something outside himself in order to love. By contrast, the triune God had no need of creation since Father, Son and Spirit have always loved one another. Creation, then, is but the overflow of their eternal love. The Trinity is also vital practically. For it rightly relates us to God by calling us to submit to all that scripture says of him, to acknowledge the limits of our understanding and to celebrate his incomparable greatness.