I believe that the doctrine of the Trinity is essential (in the sense that it is most consistent with) a theology of love. The Bible says that God is love. I am of the school of thought that LOVE is God's core characteristic. Indeed, all other 'attributes' of God are simply His love playing out in context. I believe belief in the Trinity is part and parcel with this theology.
The Father, Son & Spirit are, and always have been, a loving relationship. In trinitarian thought, love is not just something God does... love is something God is. God is a loving relationship. There was never a reality where only the Father existed. If such a time had existed, love could only be at best a potential attribute to be displayed at some future date.
In Islam, for example, God is rigidly one. He created, primarily, in order to have creation submit to Him. How could love be a core characteristic for Allah if, before creation, He was without relationship entirely? Likewise, how could the Christian God have love as a core characteristic without any essential relationship? The Christian God is love. The Christian God is the loving relationship b/w Father, Son & Spirit.