Within Latter-day Saint doctrine, simply qualifying for the Celestial Kingdom is not the same as receiving its highest blessing. Section 131 of the Doctrine and Covenants, recorded a decade after the original vision, teaches that the Celestial Kingdom itself contains three further degrees, and that reaching the highest of the three, called exaltation, requires a person to have entered the new and everlasting covenant of marriage, sealed for eternity rather than only for mortal life, typically inside a temple. Without that sealing, the revelation states, a person may still inherit a glory within the Celestial Kingdom but cannot receive its full increase, phrased in the text as being unable to have an increase of posterity in the eternities that follow.
For members, this doctrine is why temple marriage carries weight beyond a wedding ceremony: it is presented as the ordinance that makes exaltation, the fullest possible destiny the faith describes, available at all. Families sealed in this way are taught that the relationship can continue as an eternal unit rather than ending at death, framed by the church as one of the most distinctive and consequential differences between Latter-day Saint theology and the theology of most other Christian traditions, most of which do not treat marriage as an ordinance capable of extending past the grave.