Joseph Smith, the first prophet of The Church of Jesus Christ of Latter-day Saints, or Mormon Church, defined the priesthood as "an everlasting principle, [which has] existed with God from eternity, and will to eternity, without beginning of days or end of years,…holding the keys of power and blessings” (The Prophet Joseph Smith, pp. 157).
This definition needs to be explained to understand better what Mormonism means when it talks about priesthood. The priesthood is more than a group of people who directs a church. The priesthood cannot be obtained by studying religious subjects or by being a good person.
The priesthood is the power by which God governs the universe, and this power can be delegated to men (in part) according to the will of God. No one can take upon himself this power, unless it is given him by God through one of His authorized servants.
The priesthood is the power and authority by which the Church is organized and directed. By the same power, the gospel is preached and the ordinances of salvation are performed. The priesthood is also the channel through which God reveals Himself and His commandments to mankind: The priesthood holds "the key of the mysteries of the kingdom, even the key of the knowledge of God" (Doctrine and Covenants 84:19-20).
A very important characteristic of Mormonism is the belief that the priesthood can only be used in accord with the characteristics and attributes of God himself. These characteristics include persuasion, long-suffering, gentleness, meekness, love unfeigned, righteousness, virtue, knowledge, justice, judgment, mercy, and truth (see Doctrine and Covenants 121:41).
When a man tries to use this power to cover his sins, to obtain the honors of the world, to gratify his pride, or to exercise unrighteous dominion (see Doctrine and Covenants 121:33-37) he loses his priesthood power, because no man can use this power unworthily.