Each individual is a spirit child of Heavenly Father and existed as a spirit before this life on earth. During this life, the spirit of the individual is housed in a physical body, which was born of mortal parents.
The scriptures teach that at the time of physical death, the spirit does not die. It separates from the body and lives in the postmortal spirit world. At the time of resurrection, the spirit is reunited with the body, "never to be divided; thus the whole becoming spiritual and immortal" (Alma 11:45).
The scriptures also teach about the nature of spirits. Through the Prophet Joseph Smith, the Lord revealed that "all spirit is matter, but it is more fine or pure, and can only be discerned by purer eyes" (D&C 131:7). The Lord also revealed that "the spirit of man [is] in the likeness of his person, as also the spirit of the beast, and every other creature which God has created" (D&C 77:2; see also Ether 3:7–16).
—See True to the Faith (2004), 164–65
Guide to the Scriptures