The Holy Spirit (also called the Spirit of the Lord, the Spirit of God, the Spirit, etc.) is God Himself active in His creation. Just as the term spirit (see SPIRIT) carries the basic meaning of living power, so the expression "Holy Spirit" represents God especially in His creative life-giving and energizing activity. The additional description "Holy" signifies the absolute separateness and distinction of the Holy Spirit from all that is creaturely and worldly (see SANCTIFICATION, of God). "Holy" is thus essentially the equivalent of that which is divine, identifying the Holy Spirit as God.
While the distinct person of the Holy Spirit is not clearly revealed in the OT, there are indications in this direction (e.g., one's response to the Spirit equals one's response to the person of God, Isaiah 43:10-11; (cf. also Isaiah 48:16; Haggai 2:5). The distinct person of the Spirit becomes clear in the NT (cf. John 16:13), leading to the Christian understanding of the Holy Spirit as one of the three personal manifestations of God in the concept of the Trinity (see TRINITY).
In accordance with the meaning of His name, the Scriptures portray the work of the Spirit fundamentally as the Life-giver, both in the original creation and especially in the regeneration and renewing of the creation. This involves the life of non-human creation, but most predominantly the bestowal of God's life to mankind. Thus all that God is and does for His people is finally conveyed by the Spirit, whom God gives to indwell His people in direct contact with the human spirit, i.e., a fellowship of person to person.
This topic is from the Lockman Foundation.