The Holy Spirit is the third member of the Godhead. He is a personage of spirit, without a body of flesh and bones. He is often referred to as the Spirit, the Holy Ghost, the Spirit of God, the Spirit of the Lord, or the Comforter. Many believe that the Holy Spirit could even be God Himself, taking the form of a dove made of pure white light.
The Holy Ghost works in perfect unity with God and Jesus Christ, fulfilling several roles to help the humans live righteously and receive the blessings of the gospel. He “witnesses of the Father and the Son" and reveals and teaches “the truth of all things”. Christians believe that they can receive a sure testimony of God and Jesus only by the power of the Holy Ghost. His communication to their spirit carries far more certainty than any communication they can receive through our natural senses.
The Holy Spirit is also known as the Comforter. This due to the Holy Ghost acting as the soothing voice of a loving parent which can quiet a crying child, the whispering of the Spirit is said to calm even the deepest fears, hush the nagging worries of one's life, and comfort someone when they grieve. The Holy Spirit can fill one “with hope and perfect love” and “teach the peaceable things of the kingdom”.
All honest seekers of the truth can feel the influence of the Holy Spirit, leading them to Jesus Christ and his gospel. However, the fullness of the blessings given through the Holy Ghost are available only to those who receive the gift of the Holy Ghost and remain worthy.
The gift of the Holy Spirit is different from the influence of the latter. Before baptism, a person can feel the influence of the Holy Spirit from time to time and through that influence can receive a testimony of the truth. After receiving the gift of the Holy Spirit, a person has the right to the constant companionship of that member of the Godhead if he or she keeps the commandments.