Augustine in the eighth book of On Trinity begins to talk of love as involving three substances: the lover, the loved, and love. Modern apologists like Ravi Zacharias have argued that the statement God is Love could only be true if God is essentially and eternally a Triune being: the Father eternally loves the Son through the Holy Spirit. Thus, it was not that God was all alone (a monad) before the creation and had nothing to love, but being the Triune inter-personal God, He ever existed as Love.
Of course, Augustine also talks about the possibility of loving oneself and sees three things involved in this as well: “when the mind knows itself and loves itself, there remains a trinity: mind, love, knowledge; and this trinity is not confounded together by any commingling”. However, in this mono-love, there is only one person, though one may divide the experience into the lover, the loved, and love. Loving oneself is not inter-personal, and therefore possesses no love act of self-giving and submission. Therefore, the concept of the Triune God as Love is considered significant.
One objection raised to this argument goes something like this: If God is love means the Father eternally loves the Son through the Spirit, does God is Judge means the Father eternally judges the Son through the Spirit? And this applies to all statements such as “God is jealous” or “God is a consuming fire”. Is the Father eternally jealous or eternally consuming the Son? The objection tries to reduce the argument to ad absurdum.
A few clarifications are necessary. The objection misses the difference between love and the other mentioned predicates. “Jealous” here is an adjective, not a noun. “Consuming fire” is metaphorical for the righteousness of God in His judgment. “Judge” is an office which stands in relation to the created world. The statement “God is Love” is not the same as “God is Loving”. When one says that “God is Love”, there is an identity of substance and not just participation in or possessing of an attribute. This cannot be predicated of any other being. For instance, one cannot say that Mr. A is Love; we only say Mr. A is loving in nature. To say God is Love is to speak in absolute and infinite terms. The statement “God is Love” points to God as the ground of all morality and personality. Note the following excerpt from a previous post:
There are at least three approaches to understanding Trinity.
The Rational Approach. … personality finds its best explanation in the personal nature of God, whose existence as three persons (I-YOU-HE Sufficiency) in one Godhead is the ground of personhood.
The Moral Approach. It seeks to find in the doctrine of Trinity a rational ground for the absolute nature of moral virtues, such as love, goodness, and joy. If God didn’t eternally exist in a subject-object relationship, then He would be amoral and morality would not be absolute. The doctrine of Trinity provides a rational ground for any discussion of morality with respect to its absolute nature…. [See Illustrating Trinity]
Love is the summation of morality and personality and morality cannot be dissected of each other. To be a person is to be moral. Therefore, the reality of personality and morality must find an ontological ground in an infinite inter-personal Beginning and End of all things. The Triune Persons cannot be FOUR since inter-personal sufficiency is sufficed by the I-YOU-HE tri-personal Sufficiency), or else infinitude would be reduced to finite polytheism without any essential unity. Thus, the revelation of God as Love is crucial to our understanding of every other contingent reality of moral personhood.