[Philip] Schaff describes the Nicenes’ biblical arguments for the deity of the Holy Spirit:
The exegetical proofs employed by the Nicene fathers for the deity of the Holy Ghost are chiefly the following. The Holy Ghost is nowhere in Scripture reckoned among creatures or angels, but is placed in God Himself, co-eternal with God, as that which searches the depths of Godhead (1 Cor. 2:11, 12). He fills the universe, and is everywhere present (Ps. 139:7), while creatures, even angels, are in definite places. He was active even in the creation (Gen. 1:3), and filled Moses and the prophets. From Him proceeds the divine work of regeneration and sanctification (John 3:5; Rom. 1:4; 8:11; 1 Cor. 6:11; Tit. 3:5-7; Eph. 3:16; 5:17, 19, etc.). He is the source of all gifts in the church (1 Cor. 12). He dwells in believers, like the Father and the Son, and makes them partakers of the divine life. Blasphemy against the Holy Spirit is the extreme sin, which cannot be forgiven (Matt. 12:31). Lying to the Holy Ghost is lying to God (Acts 5:3, 4). In the formula of baptism (Matt. 28:19), and likewise in the apostolic benediction (2 Cor. 13:13), the Holy Ghost is put on a level with the Father and the Son, and yet distinguished from both; He must therefore be truly divine, yet at the same time a self-conscious person. The Holy Ghost is the source of sanctification, and unites us with the divine life, and thus must Himself be divine. The divine trinity tolerates in itself nothing created and changeable. As the Son is begotten of the Father from eternity, so the Spirit proceeds from the Father through the Son.
— Calvin Beisner, from God in Three Persons, p. 117