Hans Urs von Balthasar defines love in many of his texts. He was Swiss and a renowned theologian and Catholic priest. He passed away prior to being made a cardinal.
Given his education in theology and religion, Balthasar was looked to for his defining of love (both mortal love and agape--God's love). In Retrospective, Balthasar defined love in four distinct ways. First, love is the thing which defines and unites the different. It is only through love that one can accept and define those different from one's self. Second, love defines and illuminates the truly joyful and beautiful. Essentially, only when one possesses love can he or she be defined as joyful and beautiful. Third, love is defined as something good. Therefore, if one possesses love, he or she must be good as well. Lastly, love is defined as being true. Again, through the possession of love (which is true), one must be true.
Given that God is accepting, joyful, beautiful, good, and true, God epitomizes love. In a sense, Balthasar defines God's love through defining the characteristics of God himself (given a masculine gender based upon historical Christian ideology).