Mormon missionaries are referred to by the titles Elder for men and Sister for women. This is to represent the fact that they are full-time Mormon Church missionaries and as such have been set apart for a special mission. They have vowed to put dating, school, and careers on hold while they preach the restored Gospel of Jesus Christ. Men are called Elders, because they hold the office of Elder in the Melchizedek Priesthood of the Mormon Church. They serve in pairs and devote their full energies to preaching the Gospel for two years. Women in the Mormon Church do not hold priesthood offices, but nevertheless hold many important teaching and leadership positions. Since Mormons generally refer to each other as brothers and sisters, in recognition of the fact that all people are children of one Universal Father who is God, female missionaries are therefore called Sisters and serve for a period of eighteen months. All Mormon missionaries serve in pairs called companionships.