D&C 88

In revelation, the Lord provides the true definition of the "soul" -

"...the spirit and the body are the soul of man.
16 And the resurrection from the dead is the redemption of the soul."  (Doctrine and Covenants | Section 88:15 - 16)

But in the redemption of the soul, not all souls are equal in glory for  -

"They who are of a celestial spirit shall receive the same body which was a natural body; even ye shall receive your bodies, and your glory shall be that glory by which your bodies are quickened.
29 Ye who are quickened by a portion of the celestial glory shall then receive of the same, even a fulness.
30 And they who are quickened by a portion of the terrestrial glory shall then receive of the same, even a fulness.
31 And also they who are quickened by a portion of the telestial glory shall then receive of the same, even a fulness.
32 And they who remain shall also be quickened; nevertheless, they shall return again to their own place, to enjoy that which they are willing to receive, because they were not willing to enjoy that which they might have received."  (Doctrine and Covenants | Section 88:28 - 32)

For -

"they who are not sanctified through the law which I have given unto you, even the law of Christ, must inherit another kingdom, even that of a terrestrial kingdom, or that of a telestial kingdom.
22 For he who is not able to abide the law of a celestial kingdom cannot abide a celestial glory.
23 And he who cannot abide the law of a terrestrial kingdom cannot abide a terrestrial glory.
24 And he who cannot abide the law of a telestial kingdom cannot abide a telestial glory; therefore he is not meet for a kingdom of glory. Therefore he must abide a kingdom which is not a kingdom of glory."  (Doctrine and Covenants | Section 88:21 - 24)

The Lord then explains why these things are -

"For what doth it profit a man if a gift is bestowed upon him, and he receive not the gift? Behold, he rejoices not in that which is given unto him, neither rejoices in him who is the giver of the gift.
34 And again, verily I say unto you, that which is governed by law is also preserved by law and perfected and sanctified by the same.
35 That which breaketh a law, and abideth not by law, but seeketh to become a law unto itself, and willeth to abide in sin, and altogether abideth in sin, cannot be sanctified by law, neither by mercy, justice, nor judgment. Therefore, they must remain filthy still."  (Doctrine and Covenants | Section 88:33 - 35)

It all comes down to that law we are willing to abide by for -

"All kingdoms have a law given..."  (Doctrine and Covenants | Section 88:36)

The soul of all men will live in that kingdom they feel most comfortable and willing to live.