Holy Ghost; Holy Spirit

Concise Bible Dictionary:

The third Person in the Trinity, as seen in the formula of baptism (Matt. 28:1919Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: (Matthew 28:19)). The Spirit moved upon the face of the waters at the creation (Gen. 1:22And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. (Genesis 1:2)); and He came upon certain persons in the Old Testament to fulfill the purposes of God. David asked that the Holy Spirit might not be taken from him (Psa. 51:1111Cast me not away from thy presence; and take not thy holy spirit from me. (Psalm 51:11)); which stands in contrast to the indwelling of the Holy Spirit in Christians, for He abides with them. It is by the operation of the Spirit that they are born anew, and He is the seal of their faith in Christ, and the earnest of their inheritance above (John 3:55Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. (John 3:5); Eph. 1:13-1413In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise, 14Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory. (Ephesians 1:13‑14)). He is their COMFORTER or Advocate (παράκήτος, one who manages their affairs) on earth, as Christ is the same in heaven (John 14:16, 2616And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; (John 14:16)
26But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you. (John 14:26)).
Though the Holy Spirit influenced and came upon the Old Testament saints, He did not come personally until Christ had ascended (John 16:77Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you. (John 16:7)). Many passages prove His personality—a matter of great importance, often lost sight of by those who constantly speak of Him as an influence. Ananias lied to the Holy Spirit (Acts 5:33But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land? (Acts 5:3)). “The Holy Ghost said, Separate me Barnabas and Saul” (Acts 13:22As they ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have called them. (Acts 13:2)). “Dividing.... as He will” (1 Cor. 12:1111But all these worketh that one and the selfsame Spirit, dividing to every man severally as he will. (1 Corinthians 12:11)). The Holy Spirit directed the labors of Paul and his companions (Acts 16:6-76Now when they had gone throughout Phrygia and the region of Galatia, and were forbidden of the Holy Ghost to preach the word in Asia, 7After they were come to Mysia, they assayed to go into Bithynia: but the Spirit suffered them not. (Acts 16:6‑7)), and the Lord Jesus cast out demons by the Spirit of God (Matt. 12:2828But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you. (Matthew 12:28)).
His presence and operations here are some of the fruits of Christ’s exaltation. He forms Christ in the believer. He is also the power of life and the power for testimony. Indwelling the saints individually, He forms them collectively into one body, they are also builded together for a habitation of God through the Spirit (1 Cor. 3:1616Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you? (1 Corinthians 3:16); Eph. 2:2222In whom ye also are builded together for an habitation of God through the Spirit. (Ephesians 2:22)).
To be indwelt by the Holy Spirit is an immense favor, for He is a divine Person: any one so indwelt is not in the flesh, but in the Spirit. He is the Spirit of sonship and by Him the believer cries, Abba Father. Christians are exhorted to be guided by Him, and neither to quench nor to grieve that holy One. Our responsibility is to “walk in the Spirit” (Gal. 5:1616This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh. (Galatians 5:16)).

Related Books and Articles:

Holy Spirit: February 2006
The Action of the Holy Spirit in the Assembly
The Spirit of God