Start with these observations:
- Love is the most important aspect of the moral life.
- If love is the most important aspect of one's moral life, it is wrong to perform a non-obligatory action that terminates all one's loves.
- Wrong actions are not praiseworthy.
- Some non-obligatory instances of sacrifice of one's life for another are praiseworthy.
- If there is no life after death, then sacrificing one's life terminates all one's loves.
- Some instances of sacricifing one's life are neither wrong nor obligatory. (3 and 4)
- If there is no life after death, then all non-obligatory sacrifice of one's life is wrong. (1, 2 and 5)
- So there is life after death. (6 and 7)