Because He is a spirit, certain particulars of the Holy Spirit are ambiguous. Like the Father, the Spirit has never been embodied; and while we attribute the name Jehovah or Yahweh to the Father, and Jesus to the Son, the Spirit has no known name. However, the Bible gives at least eighteen different titles to the Holy Spirit, of which include: Spirit of Christ; Spirit of Grace; Counselor (Comforter, KJV), Spirit of Truth and more.
Jon Isaak writes that the Holy Spirit is:
God’s living presence among God’s people, carrying out the mission of the risen Lord Jesus, which is the creation of a new humanity….The Spirit motivates, empowers, and guides God’s people, enabling them to go beyond previous possibilities in the formation of open, sharing, and true communities of Jesus.
Therefore, the Spirit has an active role to play in our salvation. Whereas the Father desired to reconcile mankind back to himself, and made a promise and plan of salvation; the role of Jesus was to carry out salvation as the Messiah—the Lamb of God—to bear the sins of the world upon himself. The Holy Spirit then came as the ever-present form of God who calls and creates that reconciliation in our hearts today.
To accomplish this, the Holy Spirit works in the hearts of disciples, calling them to the mission of making other disciples. The Spirit then works in the hearts of sinners, to save them, and then calls upon them to make disciples.
The act of a sinner turning to a belief in the work of Christ, accepting his shed blood, and inviting the Holy Spirit in to forgive and renew himself is often called regeneration.
 Jon M. Isaak, The Holy Spirit in the Scriptures, http://web.ebscohost.com/ehost/pdfviewer/pdfviewer?vid=3&sid=9a7c0cbc-3efa-423c-98d1-4f265995b7a4%40sessionmgr198&hid=128 (accessed April 20, 2013).
- The Role of The Holy Spirit in Salvation: Part 2 (jmdansville.wordpress.com)
- The Holy Spirit: Why should we study The Holy Spirit? (jmdansville.wordpress.com)
- The Role of The Holy Spirit in Salvation: Part 1 (jmdansville.wordpress.com)