I heard it mentioned only once in the scriptures that there are 3 levels of celestial glory, but could celestial glory just mean the Telestial, Terrestrial, and Celestial Kingdoms? Because if there are 3 degrees within the Celestial Kingdom itself, who goes to what degree? Here would be my guess:
Highest degree- Sealed through marriage in temple.
Middle degree- Endowed in temple, but not married.
Lower degree- Baptized, but not endowed or married.