Love is not God. But God is love. So what does it mean for God to be love?
It does not necessarily mean that God is simply loving. Judaism and Islam and Mormonism teach a God who loves. But when Christians teach that God is himself love, they are saying that real love itself has its origin and its essence in God. And this cannot be true unless God is a Trinity.
Think about it. A solitary god cannot be love. He may learn to love. He may year for love. But he cannot in himself be love, because love requires an object. Real love requires relationship. In the doctrine of the Trinity we finally see how love is part of the fabric of creation; it is essential to the eternal, need-nothing Creator. From eternity past, the Father and the Son and the Holy Spirit have been in community, in relationship. They have loved each other. That loving relationship is bound up in the very nature of God himself. If God were not a Trinity but merely a solitary divinity, he could neither be love nor be God!
So the Trinity is not some weird religious aberration Christians have stupidly clung to. It is the answer to the deepest longing of the human heart. The Trinity answers history’s oldest desire. It even clarifies the question. It makes us go deeper than sentimental notions and ethereal feelings and elusive emotions. It puts us on solid ground with all this love stuff we’ve been chasing forever.
– Jared C. Wilson, Unparalleled: How Christianity’s Uniqueness Makes it Compelling (Baker, forthcoming) pp. 66-67.