The Spirit is, of course, scriptural as is the Incarnation.
The subjects under discussion between 318 and 381 were not, as has sometimes been alleged, those raised by Greek theology or philosophy and such as could only have been raised by a people thinking in Greek terms. It was not simply a quarrel about Greek ideas. In the fourth century there came to a head a crisis . . . which was not raised by either Arius or Athanasius. It was the problem of how to reconcile two factors which were part of the very fabric of Christianity: monotheism, and the worship of Jesus Christ as divine. Neither of these factors is specifically connected with Greek philosophy or thought; both arise directly from the earliest Christian tradition. Indeed . . . it was only by overcoming some tendencies in Greek philosophy which offered too easy an answer to the problem that a solution was reached. Greek philosophy and religion could readily accept a monotheism which included an hierarchically graded God and could easily accord a qualified divinity to the Son. Neither was in the end accepted by the church. But of course it would be absurd to deny that discussion and dispute between 318 and 381 were conducted largely in terms of Greek philosophy. The reason for this was, paradoxically, because the dispute was about the interpretation of the Bible. The theologians of the Christian Church were slowly driven to a realization that the deepest questions which face Christianity cannot be answered in purely biblical language, because the questions are about the meaning of biblical language itself. In the course of this search the Church was impelled reluctantly to form dogma. It was the first great and authentic example of the development of doctrine.
Hanson, R.P.C. The Search for the Christian Doctrine of God [Baker 1988, 2005, p. xx-xxi]
The Spirit is Gods way of being present, powerfully present, in our lives and communities as we await the consummation of the kingdom of God. Precisely because he understood the Spirit as Gods personal presence, Paul also understood the Spirit always as an empowering presence; whatever else, for Paul the Spirit was an experienced reality.
Fee, Gordon D. Gods Empowering PresenceThe Holy Spirit in the Letters of Paul [Hendrickson 1994 p. xxi]
Here was how the early church came to appropriate the salvation that Christ had brought; and here was how believers came to understand their own existence as essentially eschatological, with the Spirit as both the evidence that Gods great future for the people of God had already made its way into the present and the guarantee that God would complete the work he had begun in Christ. Thus the Spirit is absolutely presuppositional to their entire experience and understanding of their present life in Christ; and as often happens with such presuppositional matters, one rarely looks at them reflectively.
Fee, Gordon D. Gods Empowering PresenceThe Holy Spirit in the Letters of Paul [Hendrickson 1994 p. 2-3]
1 Corinthians 6:11
This is the second of such soteriological moments in Paul (2 Thess 2:13), in which Paul refers to peoples conversion in latent Trinitarian language, in which the Father saves, through the work of Christ, effected experientially by the Spirit.
Fee, Gordon Gods Empowering Presence: The Holy Spirit in the Letters of Paul [Hendrickson, 1992, 2004, p. 128]
1 Corinthians 12:4-6
The Trinitarian implications in this set of sentences, the earliest of such texts in the nt, are striking. As Barrett notes, The Trinitarian formula is much more impressive because it seems to be artless and unconscious (284). It is not actually a Trinitarian construct per se; i.e., Pauls interest is not in the unity of the Persons of the Godhead: The relationships are not spoken to at all, nor does he say that the Father, Son, and Spirit are one. Nevertheless, passages like this are the stuff from which the later theological constructs are correctly derived.
Fee, Gordon Gods Empowering Presence: The Holy Spirit in the Letters of Paul [Hendrickson, 1992, 2004, p. 162-163]