Jeff answered...

Jesus taught, "Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God" (John 3:3 KJV). This means that, in order to enter the Kingdom of God, each of us must be "born again" by being baptized and receiving the Spirit of God. The Church today administers those ordinances to anyone who wishes to receive them and makes the necessary commitments. But there have been countless billions of people who have died without the opportunity to receive those ordinances. They are not lost---God has provided a means for them to receive baptism if they so choose. Members of the Church go to the temples to be baptized in behalf of those who have died without the chance to receive baptism. Like regular baptisms, these ordinances are performed by certain persons with the authority to do so in the sight of God. This way, those who have died without baptism have the ordinance done for them, which they are free to reject or accept. Neither the Church nor its members count those dead persons who have had baptisms performed for them as "members," and neither do they regard those persons "Mormons."