Ponder the evidence as displayed by two different individuals. Both are in their golden years and both discover they have a limited time left on earth. One becomes sullen and loses his zest, retiring to a favorite chair and waits. The other accepts his fate , but continues his remaining days as a cheerful member of society. These are Interesting but predictable circumstances. Selflessness is the key.
The first individual cannot accept his fate and struggles with his mortality. Having put his needs above others all his life he no longer has purpose.
The second person who throughout his life, saw and provided for the needs of others has been gifted a glimpse of eternal life.