People who deny the perspective of eternity, and place all their hopes and faith in this life, will eventually lose all. There is nothing permanent in this world of change and decay. Such people have two alternatives: (1) short-term, careless pleasure for a moment; (2) philosophical despair. These two sad, destructive options are repeated again and again in secular literature, as consequences of the loss of faith and hope.
For who knows what is good for man while he lives the few days of his vain life, which he passes like a shadow? For who can tell man what will be after him under the sun?
-- Ecclesiastes 6:12
To set the mind on the flesh is death, but to set the mind on the Spirit is life and peace. For the mind that is set on the flesh is hostile to God; it does not submit to God's law, indeed it cannot; and those who are in the flesh cannot please God.
-- Romans 8:6-8