Ordination is based on the recipient's age and worthiness and does not require any specific training or aptitude. A candidate for this ordination is interviewed and often counseled to study the 84th, 107th, and 121st sections of the Doctrine and Covenants to begin to understand the "oath and covenant of the priesthood", the covenant a person makes with God when he receives the Melchizedek priesthood. The candidate is also usually asked to stand in a gathering of the members of the church to be publicly accepted as being worthy of ordination. For male Latter-day Saints, receiving the Melchizedek priesthood is considered to be a saving ordinance of the gospel. Shortly after the establishment of the church, the ordination of blacks to the priesthood was prohibited. Following a revelation to then-Church president Spencer W. Kimball, the church lifted the prohibition in 1978. An important purpose of giving the Melchizedek priesthood to every adult Latter-day Saint man is to allow fathers and husbands to be able to give priesthood blessings of healing, comfort, counsel, and strength to their children and wife, and to preside over the family unit in a righteous manner. Many LDS fathers give a priesthood blessing to their children before the start of each new school year or before an important life event such as marriage. Each Melchizedek priesthood bearer, regardless of priesthood office, is encouraged to give priesthood blessings when called upon by others. In the LDS Church, there are five offices within the Melchizedek priesthood. Although the holders of the different priesthood offices hold the same Melchizedek priesthood, their assigned rights and responsibilities vary according to their priesthood office. Holders of priesthood offices are organized into quorums. The quorums are a brotherhood where members of the quorum assist each other, teach one another, and delegate particular responsibilities to individuals or committees. Members of the church who do not maintain the standards and people who are not members of the church are invited to participate in the quorum to enjoy the brotherhood and support, although they may not be given certain quorum responsibilities. In order to be called to the Aaronic priesthood office of bishop, a man must either be a literal descendant of Aaron or, more commonly, be "a high priest of the Melchizedek Priesthood". Each quorum and organizational unit in the church has a presidency attached to it. A presidency is usually composed of three members: the president and two counselors. Typically, a president is selected and he chooses the two counselors whom he would like to serve with him.