That love is the product of the Father's love for Christ and Christ's love for the Father is from Augustine, et. al.. In his book, "The Moral Quest: Foundations of Christian Ethics," Grenz basically states that same thing. It of course is not correct, but ...
Augustine notes that the Spirit can apply to both the Father and the Son but can also be the third Person. In terms of relationship Augustine sees the Spirit as a Gift of both the Father and Son who are the Giver (Acts 8:20; Rom 5:5; John 4:7). Thus Augustine derives his immanent procession of the Spirit from the Father and the Son from an economic procession. Augustine was most concerned, however, to understand the nature of the Godhead independently of the economy of salvation. In this respect he described the Spirit in terms of love between the Father and the Son. He identifies the Spirit with love, by arguing that God’s greatest gift is both love and the Spirit. Therefore the Spirit is love. The Father is the one who loves the Son; the Son is beloved by the Father; and the Spirit is the bond of love between them.
The Concise Oxford Dictionary of The Christian Church says it differently, but ...I think it is suppose to mean the same thing ...
Christianity affirms that God is a Trinity, consisting of "three persons in one substance", the Father being the source of all existence, the Son the Eternal Object of the Father's love and the Mediator of that love in creation and redemption, and the Holy Spirit the Bond of Union between the Father and Son
and in his "Three Philosophies of Life: Ecclesiastes," Peter J. Kreeft says, "The love between the Father and Son is so alive that it lives a life of its own, a Person in its own right, the Third Person of the Trinity." (page 107, Song of Songs, Life as Love). <img src="/forum/images/graemlins/Banghead.gif" alt="" />
And there are yet others that say God = the Father, Jesus = the Son, and the Holy Spirit = the mother.