Pneumatology is the branch of systematic theology that treats the doctrine of the Holy Spirit—His deity and personhood as the third person of the Godhead, His eternal procession from the Father and the Son, and the whole range of His work in creation, revelation, regeneration, indwelling, sanctification, illumination, sealing, and the gifting of the church. The Spirit is no impersonal energy or divine influence, but very God, co-equal and co-eternal with the Father and the Son, sharing the one undivided divine essence while subsisting as a distinct person. From the brooding of the Spirit over the waters at creation, through the inspiration of the prophets, to the conception of Christ, His anointing for ministry, His resurrection by the Spirit, and the outpouring at Pentecost, the Holy Ghost is everywhere active in the unfolding of redemption. He applies to the elect all that Christ purchased: convicting of sin, working the new birth, uniting the believer to Christ, dwelling within as the down-payment of glory, producing His fruit, and conforming the saint to the image of the Son. A sound pneumatology guards against two perennial errors—the neglect that forgets the Spirit and quenches His work, and the excess that exalts spectacular experiences above the Word and the cross. The Spirit, the Lord and Giver of life, never speaks of Himself but glorifies Christ; therefore right doctrine of the Spirit always issues in the magnifying of the Savior to whom the Spirit bears witness.