According to the New Testament “God is love” (1 John 4:8). But according to historic Christian theology God is love only because God is a Trinity. In fact, Christian theology asserts that God can only be a supreme independent being exactly because God is a Trinity. This insight led British evangelical theologian Bruce Milne to state that “just about everything that matters in Christianity hangs on the truth of God’s three-in-oneness.”1
In traditional monotheism (classical Judaism, Islam, and Unitarianism), God is one being and one person. Or, philosophically, God is one What (essence) and one Who (person). Thus the one God is a single, solitary person. But this common conception of monotheism raises serious theological difficulties.
If God is a single, solitary person (like the Jewish conception of Yahweh and the Islamic conception of Allah), then traditional monotheism must answer two fundamental questions:
1. Who did God love in eternity before he created the world?
2. Is God in desperate need of the creation to fulfill himself?
On this view, before God created he––as a single person––was completely alone in eternity. God had no one to love but himself. But self-love can be toxic and it is certainly not as rich and vibrant as having love for someone else. Therefore in traditional monotheism, God must create other persons (angels or humans) in order to have someone to love. But if this were true, then God would be dependent upon the creation for fulfillment.
British evangelical theologian Michael Reeves uses the example of Allah and his title as “The Loving” in Islam to show the problem.
If Allah needs his creation to be who he is in himself (“loving”), then Allah is dependent on his own creation, and one of the cardinal beliefs of Islam is that Allah is dependent on nothing.2
Historic Christianity’s Trinitarian monotheism holds that God is one being and three persons. Or philosophically stated, God is one divine What (essence) and three Whos (three distinct, but not separate persons: Father, Son, and Holy Spirit). Thus the one God has eternally existed as a community of persons.
In Christianity, God is principally a Father who forever loves his Son and Spirit in eternity before the creation of all contingent things. The Triune God has existed forever in an eternal community of loving relationships. That love then spilled over when God created all things. Therefore God is love and is capable of loving his creatures precisely because God is a Trinity.
One of the most beloved, gospel-summarizing Bible verses takes on new meaning when understood through a Trinitarian prism:
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. (John 3:16)