Everything we achieve in life is temporary. Biological purposes of living like survival and reproduction are easily negated by mortality. Survival is only the postponement of death, which is ultimately inescapable, and reproduction only serves to continue one's genetic lineage, which is impossible to maintain forever. Happiness as the purpose of life is also negated by death. Tolstoy draws upon an eastern fable to explain this, wherein a traveller finds himself hanging from a branch above the jaws of a dragon. Two mice, one white and one black, gnaw away at the other end of the branch. Knowing he will die, the traveller notices some drops of honey on a leaf of the branch and licks them. The dragon is death, the white and black mice are day and night bringing the traveller closer to his end, and the honey is the pleasures and happiness of life. Tolstoy, being deeply aware of his death like the traveller above the dragon, can no longer enjoy the 'honey' of life, calling the joys of life 'delusions' to distract him from the inevitability of death. In this view, life has no true purpose as anything achieved is temporary and anything experienced is merely a distraction in the path toward death.
Life is not about trying to make things which will last forever; it is about the things we do while we are alive. A life enrichened by valuable experiences and achievements is not purposeless just because it ended. Death may even be what gives life its meaning and purpose. Without death, humans would be unmotived to take any actions. Having a limited amount of time to live motivates us to live our lives more fully, otherwise, any action could be postponed forever.
Rejecting the premises