Very early in the Old Testament, we learn that God established a priesthood for His church. The Aaronic Priesthood was given to the family of Aaron who met certain requirements, including being males without blemish.
Many portions of the New Testament gospel were lost after the deaths of Jesus and His apostles. In the 1800s, Joseph Smith was called by God to assist in the restoration of the fullness of the gospel. This restored church is called The Church of Jesus Christ of Latter-day Saints, and some people call the members of this church Mormons because they use the Book of Mormon in addition to the Bible.
Because there had been no prophet, and God had taught in the Bible that His church would be built on a foundation of apostles and prophets, the priesthood of God was among those things that was lost. Without a prophet, the keys (symbolic keys representing authority from God), no one could be called to be a priesthood holder.
Joseph Smith was given ancient plates by an angel who had hidden them during his mortal life. They contained a religious record of an ancient people in the New World who were visited by Jesus Christ after His death and resurrection. Joseph was assigned to translate them through the spirit of God, and during this process, he encountered scriptures about the importance of baptism. He and his scribe, Oliver Cowdery, went to the woods to ask how they should be baptized. John the Baptist appeared to them, being the person so important to baptism that he was even chosen by Jesus for His own baptism. John held the keys to baptism that had been taken from the earth during apostasy.
A person must hold the Aaronic Priesthood in order to baptize, so John gave them the Aaronic priesthood, restoring that to the earth. When they had it, they were able to baptize each other. Baptism must be carried out by a mortal person on earth.
This Aaronic priesthood is sometimes called the preparatory priesthood because it helps the holder prepare for higher levels of priesthood. It is given to all worthy boys or men who are at least twelve years old. (We must remember that God did not give the priesthood to women in the Bible because it is assigned to men, in the same way only women are allowed to give birth. Neither restriction is discriminatory, but merely an assignment of roles chosen by God.)
The Aaronic Priesthood has three levels. The first, held by boys ages twelve and thirteen (or by men and boys who receive it later than these ages) is the office of Deacon. A deacon passes the Sacrament (communion) to the members of the congregation. During the basic worship service they provide any service the bishop (lay pastor) may require and sometimes also collect fast offerings. Fast offerings result from members who are physically able going without food or drink for two meals and then donating the money saved—the offering—to a special fund used to care for the poor in the congregation.
Fourteen and fifteen year old boys may be teachers. This does not mean they teach a class. It means they can be home teachers. Every family in a congregation is assigned two men to visit them at least monthly to deliver a spiritual message and to watch over their temporal welfare. For instance, if the home teachers notice the family does not have enough to eat, they will inform the bishop so he can step in to help. The home teachers are the first people a family calls when they need help. Teachers also prepare the Sacrament bread and water before the service begins. In addition, they can do anything a deacon can do.
Sixteen and seventeen year old boys can be priests. These young men may baptize, bless (pray over) the Sacrament, and ordain other boys or men to the offices of the Aaronic priesthood they already hold. They can also perform the services of a deacon or teacher.
At age eighteen, most young men receive the Melchizedek priesthood. This priesthood is named after the Biblical Melchizedek. The first level of this priesthood is that of elder. Elders may serve full-time two year missions for the church and during these missions they are known by the title of Elder. At other times, they do not use the title. (Women may also serve missions but do not require the priesthood, of course, to do so.) They may confirm someone a member of the Church, heal the sick, and perform other duties of the priesthood. Some men also receive other levels of priesthood, including that of High Priest, the priesthood level required of a bishop or other high level priesthood leadership position. Women who serve in high level positions do not need the priesthood, which is only given to men. Men must hold the Melchizedek priesthood to enter the temple; women can enter it without needing the priesthood.
The priesthood is not a paid position. The Mormons have a lay church and everyone volunteers his or her time. This is a position of service, allowing the holder to serve people in some specific ways a person without the priesthood cannot. However, the church offers many ways for every member to serve the church, its members, and the community.
Men who hold the priesthood may not use it to benefit themselves. They may only use it to bless others. If they need a priesthood ordinance, such as the healing of the sick, they must ask two other priesthood holders to give it. They may not give it to themselves. Women may receive these blessings and are not denied any blessing that results from the priesthood. They simply receive those blessings in other ways. While a priesthood holder must commit to live the gospel and represent God well, women are expected to do the same, without needing the priesthood to help them do it. Expectations for men and women are the same, even when they are carried out in different ways.
The priesthood does not come with self-generated powers. It is only the power to act in God’s name and according to His will. The priesthood holder does only those things he has been commanded by God to do and must do them in His own way. This means it is not a position of power, since the priesthood holder, of himself, has no power. Men who hold it understand it is a responsibility. Both men and women are taught to honor the priesthood and what it represents.