Holy Ghost In Scripture.
In the New Testament the word spirit and, perhaps, even the expression spirit of God signify at times the soul or man himself, inasmuch as he is under the influence of God and aspires to things above; more frequently, especially in St. Paul, they signify God acting in man; but they are used, besides, to designate not only a working of God in general, but a Divine Person, Who is neither the Father nor the Son, Who is named together with the Father, or the Son, or with Both, without the context allowing them to be identified.
A few instances are given here. We read in John, xiv, 16, 17: “And I will ask the Father, and he shall give you another Paraclete, that he may abide with, you for ever. The spirit of truth, whom the world cannot receive“; and in John, xv, 26: “But when the Paraclete cometh, whom I will send you from the Father, the Spirit of truth, who proceedeth from the Father, he shall give testimony of me.” St. Peter addresses his first epistle, i, 1-2, “to the strangers dispersed . . . elect, according to the foreknowledge of God the Father, unto the sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ”. The Spirit of consolation and of truth is also clearly distinguished in John 16:7, 13-15, from the Son, from Whom He receives all He is to teach the Apostles, and from the Father, who has nothing that the Son also does not possess. Both send Him, but He is not separated from Them, for the Father and the Son come with Him when He descends into our souls (John 14:23).
Many other texts declare quite as clearly that the Holy Ghost is a Person, a Person distinct from the Father and the Son, and yet One God with Them. In several places St. Paul speaks of Him as if speaking of God. In Acts 28:25, he says to the Jews: “Well did the Holy Ghost speak to our fathers by Isaias the prophet“; now the prophecy contained in the next two verses is taken from Isaias 6:9-10, where it is put in the mouth of the “King the Lord of hosts”. In other places he uses the words God and Holy Ghost as plainly synonymous. Thus he writes, I Corinthians 3:16: “Know you not, that you are the temple of God, and that the Spirit of God dwelleth in you?” and in 6:19: “Or know you not, that your members are the temple of the Holy Ghost, who is in you . . . ?” St. Peter asserts the same identity when he thus remonstrates with Ananias (Acts 5:3-4): “Why hath Satan tempted thy heart, that thou shouldst lie to the Holy Ghost . ? Thou hast not lied to men, but to God.” The sacred writers attribute to the Holy Ghost all the works characteristic of Divine power. It is in His name, as in the name of the Father and of the Son, that baptism is to be given (Matt. xxviii, 19). It is by His operation that the greatest of Divine mysteries, the Incarnation of the Word, is accomplished (Matthew 1:18, 20; Luke 1:35). It is also in His name and by His power that sins are forgiven and souls sanctified: “Receive ye the Holy Ghost. Whose sins you shall forgive, they are forgiven them” (John 20:22-23); “But you are washed, but you are sanctified, but you are justified in the name of our Lord Jesus Christ, and the Spirit of our God” (I Corinthians 6:11); “The charity of God is poured forth in our hearts, by the Holy Ghost, who is given to us” (Romans 5:5). He is essentially the Spirit of truth (John 14:16-17; 15:26), Whose office it is to strengthen faith (Acts 6:5), to bestow wisdom (Acts 6:3), to give testimony of Christ, that is to say, to confirm His teaching inwardly (John 15:26), and to teach the Apostles the full meaning of it (John 14:26; 16:13).
With these Apostles He will abide for ever (John 14:16). Having descended on them at Pentecost, He will guide them in their work (Acts 8:29), for He will inspire the new prophets (Acts 11:28; 13:9), as He inspired the Prophets of the Old Law (Acts 7:51). He is the source of graces and gifts (I Corinthians 12:3-11); He, in particular, grants the gift of tongues (Acts 2:4; 10:44-47). And as he dwells in our bodies sanctifies them (I Corinthians 3:16; 6:19), so will and them raise them again, one day, from the dead (Romans 8:11).
But he operates especially in the soul, giving it a new life (Romans 8:9 sq.), being the pledge that God has given us that we are his children (Romans 8:14-16; II Corinthians 1:22; 5:5; Galatians 4:6). He is the Spirit of God, and at the same time the Spirit of Christ (Romans 8:9); because He is in God, He knows the deepest mysteries of God (I Corinthians 2:10-11), and He possesses all knowledge. St. Paul ends his Second Epistle to the Corinthians (13:13) with this formula of benediction, which might be called a blessing of the Trinity: “The grace of our Lord Jesus Christ, and the charity of God, and the communication of the Holy Ghost be with you all.” 1914 Catholic Encyclopedia