See commentary on Alma 34:33. This life is a probationary estate, a time of testing, trying, and proving. Those who keep this their “second estate shall have glory added upon their heads for ever and ever” (Abraham 3:26). Those who use their mortal probation unwisely, having had what God judges to be a complete and fair chance to accept the gospel and the covenants of salvation, will not have that chance restored to them in the spirit world. Though they may accept the gospel there, to their everlasting benefit, they will have forfeited the chance for exaltation.
Assuming they lead honorable lives in mortality, their promise is that of terrestrial glory (see D&C 76:73-75). Joseph Smith declared the doctrine poetically as follows:
These are they that are hon’rable men of the earth; Who were blinded and dup’d by the cunning of men; They receiv’d not the truth of the Savior at first; But did, when they heard it in prison, again. Not valiant for truth, they obtain’d not the crown, But are of that glory that’s typ’d by the moon: They are they that come into the presence of Christ, But not to the fulness of God, on his throne.
(In Lyndon W. Cook, The Revelations of the Prophet Joseph Smith [Salt Lake City: Deseret Book Co., 1985], p. 164.)