Basil of Caesarea was a so-called "Spirit-fighter," that is to say someone who sought to emphasize the divine nature of the Holy Spirit. At the time when Basil wrote his most famous work, On the Holy Spirit, many Christian theologians accorded the Holy Spirit a subordinate role within the Trinity, deeming it worthy of honor, but not on the same level as that given to the Father and the Son.
Basil sought to change this attitude, arguing that the Holy Spirit, in keeping with the formula agreed at the landmark Council of Nicaea, was consubstantial with the Father and the Son. This meant that God the Father, Jesus Christ, his only begotten son, and the Holy Spirit, consisted of three divine persons in one substance. The Nicene Creed was by no means universally affirmed, and orthodox theologians such as Basil had to argue forcefully for the Holy Spirit's divinity in the face of continued skepticism.
To this end, Basil maintains that the Christian believer is saved by the grace of baptism, which comes from the Father, the Son, and the Holy Spirit. If we regard the Holy Spirit as something less than divine, as many theologians did in Basil's day, then it becomes impossible to see how anyone can truly be saved. After all, it was Christ himself, who, according to Matthew 28:19, originally commissioned the apostles to baptize "in the name of the Father, and of the Son, and of the Holy Spirit."
For Basil, then, the divinity of the Holy Spirit is inextricably linked to the question of salvation. The Holy Spirit only acts in our lives the way it does—creating and saving—because it is God. The Bible, at various points, clearly states that the Holy Spirit is the Sanctifier, the Comforter, the Advocate. These are all functions one normally associates with God. That being so, it makes no sense to insist that the Holy Spirit is somehow a subordinate partner in the Divine Economy.