"The ’first death,’ which was suffered by Adam and Eve upon their banishment from the Garden of Eden, is described by Alma as being ‘cut off both temporally and spiritually from the presence of the Lord’ (D&C 29:41; Alma 42:7-11). The parents of the human race were not the first to suffer such a ’death,’ for it had been previously decreed for Lucifer and those spirits who chose to follow him in rebelling against righteousness (D&C 29:36-37; Rev. 12:7-9; 2 Ne. 2:17-18).
“President Joseph Fielding Smith said this ’death ... has passed upon all men who have remained unrepentant and who have not received the gospel. Those who have suffered the first spiritual death or departure, which is a shutting out from the presence of God, have the privilege of being redeemed from this death through obedience to the principles of the gospel. Through baptism and confirmation they are born again and thus come back into spiritual life, and through their continued obedience to the end, they shall be made partakers of the blessings of eternal life in the celestial kingdom of God.’ (DS 2:222-23; italics added.)” (Hoyt J. Brewster, Doctrine & Covenants Encyclopedia, p. 184)
Bruce R. McConkie
“Thus ’all mankind,’ meaning all who have arrived at the years of accountability, are spiritually dead, and they so remain until they attain unto spiritual life through baptism and the receipt of the gift of the Holy Ghost.” (Mormon Doctrine, p. 757)