Ezekiel 18:4:  Behold, all souls are mine; as the soul of the father, so also the soul of the son is mine: the soul that sinneth, it shall die.

This Gem emphasizes that the soul of every person is owned by Heavenly Father.  This means it is Heavenly Father that sets the rules and it is Heavenly Father that decides if his rules have been followed.  When it comes to sin, Heavenly Father's rule is "the soul that sins, dies".  The death of a soul implies much more than physical death.  It implies spiritual death.