The Holy Ghost
Mormons believe in the Godhead, rather than the Trinity, which is to say that they believe in the Father, Son, and the Holy Ghost, but do not believe that they are three aspects of the same God. Rather, they believe that the Father, Son, and the Holy Ghost are three distinct persons, united in will and purpose.
The Holy Ghost, or Holy Spirit, is the third member of the Godhead and the only one that does not possess a body. (The other two, in Mormon belief, possess bodies of flesh and bone.) His influence can be felt everywhere, by everyone, and His purpose is to testify of the truth and power of the Gospel. He bears witness of Jesus Christ and of all truth. Beyond acting as a witness, the Holy Ghost also purifies our hearts and our minds, and helps us to develop the worthiness to return unto God, the Father.
Mormon doctrine makes a distinction between this influence of the Holy Ghost, that influence that everyone can feel if they’re open to it, and the gift of the Holy Ghost. The gift of the Holy Ghost is a sacred ordinance performed after a person’s baptism. That person is confirmed a member of the Church, and then receives that gift of the Holy Ghost. What is it? It is the privilege of having the Holy Ghost with you always. The Holy Ghost will act as a constant companion, to guide, inspire, and teach. Again, the Holy Ghost’s influence can be felt outside of the gift. The Book of Mormon, for example, promises us that the Holy Ghost will show truth to anyone who prays sincerely about it. But the influence, in such cases, is temporary and leaves shortly after the manifestation. The gift, conversely, allows us to have this influence in every moment in our lives, if we remain worthy.
Again, this gift comes after baptism into the Mormon Church, which is properly called the Church of Jesus Christ of Latter-day Saints (and Mormons believe it to be Christ’s Church restored to the earth). And this gift comes through the laying on of hands by one with the authority of the priesthood, which is the power to act in God’s name. The Holy Ghost will thereafter be a blessing in the person’s life, although He cannot remain with an unworthy person.
Why is the gift of the Holy Ghost essential? Jesus Christ has told us, in John 3:5, that "Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God" [emphasis added]. Both are necessary to return to God, both baptism and the gift of the Holy Ghost are necessary for our sanctification. With the Holy Ghost’s companionship, we can be cleansed daily of sin and ever reminded of what choices are correct. We are aided in our sincere efforts to obey God’s commandments and become more like Christ.
Another one of the beliefs of Mormonism on this matter is that spiritual truths can’t be wholly understood, unless taught and confirmed by the Holy Ghost. Therefore, members of the Mormon Church try to behave in such a way that the Holy Ghost will not leave them, which allows them to be taught and to teach by the Spirit.
The Spirit also brings us peace and comfort. He can lift our burdens, give us consolation and courage, make our personal faith stronger and increase our hope, and reveal that which we wish to know unto us.
For faithful members of the Church, the Holy Ghost is uplifting and a source of spiritual power. Because of the importance of the Holy Ghost and the witness He gives unto us, Jesus taught that no sin is greater than that against the Holy Ghost (Matthew 12:31-32). Mormons reverence this gift and try sincerely to be worthy of His companionship always.