Considering the two facts that a: God is the source of all that was, is, and evermore shall be, He is very important, and b: He is Trinity, then the Holy Trinity is of utmost importance.
Believing in the Holy Trinity is, therefore, a big deal. And I mean actually believing — belief not merely as the assent of the mind or the conceptualisation in the brain, but the actual trust and reliance upon something, trusting on something so much that it changes your worldview and lifestyle. While it’s true that some people who claim to be Trinitarian believers are boors, jerks, and swear-word worthy, their boorishness is not related to the doctrine of the Trinity one whit. Indeed, it runs entirely counter to it.
As Trinity, as three persons “with” one substance, God is an ultimately (ontologically, even?) relational being. His being is one of communion, and I think there is an importance difference between communion and community, for we are all part of various types of community from clubs to professional organisations to neighbourhoods, but communion is a much deeper connection, a stronger union and interaction of persons than community. And God, being Trinity, is communion.*
If the root of the universe is a being who is communion, and if we start taking this fact seriously (as well we should, since we were made in the very image of this Holy Trinity), then how we live changes. We will discover our own ultimate personhood through communion with God and with one another.
Fellow human beings will not be entities for exploitation, but fellow-sojourners to be embraced. Relationships will be taken seriously. Mere community, while acceptable at some times and places, will not be enough for some relationships and communities — some form of communion will become necessary for the community to be remade in the image of God.
And if the root of the universe is a being who is a monad or a simple One or not even actually a personal being, the communion is deprived of potency. Who cares? I mean, we’re all for community. But deeper connections are not necessarily where our personhood will play itself out fully. The concept of surrendering myself to another so that I may be free is not present at the root of a universe wherein the Ultimate Cause is not Trinity, is not a Being of self-giving love. I think the ramifications are many.
A second matter, besides the whole issue of communion and personhood, is the matter of worship. The Holy Trinity is ineffably sublime. When I read the Fathers about the Trinity, I am taken to greater heights of awe, wonder, and worship. This is a God to whom I would give glory. If God is a modalist God, or a monad, or a unitarian God, or the spirit of a dead man from another planet, he is less than the revelation of God found in Scripture. Far less worshippable, this much is certain.
And it is from worship of the most Holy Trinity, He Who Is three, the three-in-one, the Unity in Trinity, three co-equal and co-eternal Persons, that my desire to live according to this God’s Way stems. Why follow a lesser God? Commitment to other views of God may be deep and even total, but the question of priority is thrown into stark contrast. I can’t express it properly, but I cannot see an abandonment of the Trinity without grave implications for the life of holiness in all its matters of morality, ethics, and discipline.
This is a plea. Take the doctrine of the Trinity seriously. Read up on how truly amazing He is. Stand in awe of Him. Worship Him. And model your life upon the life He has shown unto us in His revelation.
*For a better and unmangled (and very long) explication of this, see the Eastern Orthodox theologian John D. Zizioulas, Being As Communion.