Some studies say that Spirit is the eternal essence of God because God is Spirit; so, is this Sprit the same third Person of the Trinity? But God is also love. St. Augustine said that the Holy Spirit is the bond of love that unites the Father and the Son. Is it so; or is it that the Holy Spirit is not necessarily the bond of love, but is a Person of the Trinity that is equally united with the Father and Son?
God, the Father, the Son and the Holy Spirit are three persons of the Trinity. Each is a Spirit and all three are One. When we say God is love, we attribute this trait to each one of the Hypostases, to God the Father, the Son and the Holy Spirit. What St. Augustine said is, "The Holy Spirit is specially called Love, although Not Only the Holy Spirit in the Trinity is Love." We can say that God the Father is the Lover, God the Son is the Love and God the Holy Spirit is the Spirit of Love.