Don't confuse with degrees of glory. Often misunderstood and confuse with rewards by works. See file Degrees of Glory. The term salvation is an extremely broad term.
Salvation is a gift.
All will be resurrected, even the wicked. The plan of salvation existed and was planed before the foundation of this world. In general terms salvation is the inseparable connection of body and spirit so that the resurrected persons body lives forever. The levels of salvation mentioned are the symbolic levels of glory. The scriptures tell that in the resurrection their will be one glory of the star another glory of the moon and another of the Sun.