Joseph Smith taught, "In the celestial glory there are three heavens or degrees; And in order to obtain the highest, a man must enter into this order of the priesthood [meaning the new and everlasting covenant of marriage]; And if he does not, he cannot obtain it. He may enter into the other, but that is the end of his kingdom; he cannot have an increase. (D&C 131:1-4)" Joseph Smith also taught,
There are certain blessings only available to those who are married by the Priesthood Authority only held in The Church of Jesus Christ of Latter-day Saints. In regards to these blessing the Lord has stated,
The Lord taught this doctrine to His ancient Apostles when He said, "And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven. (Matt. 16:19)"