I'll tell you who I think the Holy Spirit is. Bare with me please. I'm usually a bit wordy.
As it relates to holiness, I for much of my life was stumped as to what that really meant. Here's why: the definitions of holiness that I most often encountered in church attendance, in my studies, and at university and seminary; and what other places I encountered it, were predominately ones of consecration: being set apart from all unrighteousness, being drawn near to the purposes of God, absolute otherness; you get the picture. While those definitions seemed to apply somewhat to me, they seemed wholly inadequate when speaking of God; for they seemed to make God dependent on creation to himself be Holy; for what is God in his absolute being set apart from, if not creation? What is there for him to draw near to him other than his creatures? What in eternity is he completely other than, when all I've ever been taught is that God is eternal and we're not? Those questions set me on a quest to discover what the holiness of God was really like.
Along the way I came across obscure definitions of holiness that did seem to suffice when plugged into the heart of God: awful or absolute moral perfection. For a while I could accept those concepts. Then I was introduced to Trinitarian theology through my studies at Fuller Theological Seminary, whose thrust, as I've told you, are the interpersonal relations of the Son with the Father and the Father with the Son as portrayed in the life of Jesus, and how those relations extend into the Capadocian formulae of perichoresis ~ the interaction ~ between and within the Trinity, and how they extend to include us via the work of the Holy Spirit.
Here is what I discovered: when reading Jesus, he, seems to make clear that the only true interpretation of the Father is through the Son; nothing else will suffice to draw us into a true understanding of God as he really is. And indeed there is no knowledge of God except as revealed to us in the Father/Son relationship, not even things extrapolated from the Hebrew Scriptures; for in these latter days God has spoken to us in most apprehensively through his Son. That is to say that God, as he really is, is only revealed by the Son.
Bam! Then it hit me: absolute moral perfection: i.e., holiness, is not to be discovered in and then defined by OT Law: Do this. Don't do that. But it is given definition by Jesus, as he relates to his Father in Love, Adoration, and Prayer; respect, righteousness, and fellowship. All things began to come together. Holiness in the heart of God is the love of the Father for the Son and visa verse. It is the respect they share for each other, the absolute harmony of their righteous wills. It is the beauty, the glory, the honor we see displayed in their relations. It is their humility as revealed to us in the Son's condescension to dwell among us that revealed as well the true heart of the Father for creation through a servant's heart for humanity. And most emphatically it's a love so bonded, so bounded, so invasive, so compelling, SO INCLUSIVE that it drove them to the cross for the sake of those whom they mutually loved and willed to bring into their embrace.
In short, holiness is not assent to an absolutely untenable moral code, which can only produce an aw-ful experience of God. Holiness is that inner relationship of God. It is the practical application of that love as we live Jesus’ life, lived out in us through Christ in us the hope of Glory. It is Paul saying, "I, yet not I live but Christ ..."
Bam! a second epiphany. The "Holy" Spirit is the conduit of that mutual adoration -- Yes, proceeding from the Father to the Son, Yes, proceeding from the Son to the Father, Yes, proceeding from them both to us to include us in the reciprocity of that love.