The power and authority to act in the name of God is called priesthood. This is the power that God uses to perform His work, and it is eternal. God used the power and authority of the priesthood to create the earth, the heavens, and the entire universe. This is the power through which He keeps perfect order in the universe.
Heavenly Father delegates His priesthood power to worthy men on earth. With the power and authority of the priesthood, these men are enabled to act in God's name to bless the human family. With the priesthood, men are authorized to preach the gospel, administer the ordinances of salvation and govern God's kingdom on earth.
Priesthood authority is necessary to act in the name of God in performing baptisms, confirmations, and temple marriages and in administering the sacrament. Even though a man may be sincere, the Lord will not recognize ordinances he performs if he does not have priesthood authority. Priesthood ordinances must be performed on earth by men holding proper priesthood authority.
Priesthood power and authority are also required for presiding in The Church of Jesus Christ of Latter-day Saints and to direct the work of the Church. Jesus Christ chose His Apostles and ordained them while He lived on earth. He gave them the power and authority to act in His name and to lead His Church. Priesthood is also needed on the earth so that we can understand God's will and do His work. God reveals His will to His prophets. The current prophet serves as President of the Church and also as God's spokesman for all people in the world.
The order for receiving the priesthood was given in the days of Moses. Hebrew 5:4 says, "And no man taketh this honour unto himself, but he that is called of God, as was Aaron." Moses was Aaron's priesthood leader and ordained him in the priesthood. In the same way, a worthy male of the Church receives the priesthood "by the laying on of hands by those who are in authority, to preach the Gospel and administer in the ordinances thereof" (Article of Faith 1:5). Men cannot take priesthood authority on themselves nor can they buy and sell this power and authority.
The priesthood is here upon the earth to bless the lives of God's children and should be exercised in love, kindness and righteousness. Righteous priesthood holders who use the priesthood to bless others are promised great blessings.
Every man who righteously exercises the priesthood "will find his life sweetened, his discernment sharpened to decide quickly between right and wrong, his feelings tender and compassionate, yet his spirit strong and valiant in defense of right; he will find the priesthood a never failing source of happiness - a well of living water springing up unto eternal life" (David O. McKay, Teachings of Presidents of the Church: David O. McKay, , 116).
There are two divisions in the priesthood: the Melchizedek Priesthood and the Aaronic Priesthood. The Melchizedek Priesthood was named for Melchizedek, a great high priest, to avoid using the name of Christ too frequently. The lesser priesthood, known as the Aaronic Priesthood, is an appendage to the Melchizedek Priesthood. It was conferred on Aaron and his sons throughout all their generations and thus bears his name.
Melchizedek Priesthood holders have the power and authority to lead the Church, direct missionary work worldwide, and administer all the spiritual work of the Church. The President of the Church is the presiding high priest over the Melchizedek priesthood. Holders of the Aaronic Priesthood have authority to administer the outward ordinances of baptism and the sacrament.