Jesus was God incarnate. Yet he continually referred to, and prayed to, God the Father as someone who was distinct from himself. He also continually referred to, and claimed to be empowered by, God the Holy Spirit as someone distinct from himself. And yet Jesus, along with all Jews of his time, believed there is only one God.
Put all of this together and you arrive at the revelation that the one true God somehow exists as Father, Son, and Holy Spirit. God is, in some profound sense, eternal loving community. This is what is traditionally referred to as the Trinity, and while this term is never used in the New Testament, one finds evidence of the communal nature of God throughout the New Testament.
To me, this is the most beautiful and profound truth revealed in the NT. In fact, I’d argue it’s the most beautiful and powerful concept in all of history! For the doctrine of the Trinity magnificently expresses the truth that God is love (1Jn 4:8,16). Love isn’t merely an attribute God has. Nor is love merely an activity God does. Love is what God eternally is.
Love can only exist between persons, which is why only a God who eternally exists as a community of persons can be said to be love in and of himself. A God who existed as a single consciousness in the midst of absolute nothingness before creating the world could not be said to be love. Love could not be the essence of this solitary God. This solitary God would need to create other persons in order to begin to love. But this is not the case for the triune God revealed in Jesus Christ.
The Trinity is the only view of God that can claim that God never started loving and that God will never stop loving, for this is the only view of God in which God is intrinsically and eternally loving—whether he decides to create a world outside of himself or not.
The revelation that God is triune is the revelation that love is not merely a verb that God does; it’s the noun that God is. God always does the verb because God always is the noun. God is and always has been love. And therefore God is and always has been loving.