'The Wind blows wherever it pleases....' (John 3:8). There is certainly the sense of mystery here. We can not quantify the Spirit or comfortably explain how and when and s/he works. That s/he does work, we do not doubt. She is Christ's gift to us from the Father. The east and the west have differed in terms of whom they think sent the Spirit. The East have thought s/he proceeds from the Father and the west from the Father and the Son.
I wonder what these models have done for our articulation of the Spirit and whether in some of our expressions of Christianity, the Spirit is thought to be somewhat subordinate to the Father and the Son?