Considered on its own human life is ephemeral:
The life of mortals is like grass,
they flourish like a flower of the field;
the wind blows over it and it is gone,
and its place remembers it no more. (Psalm 103)
But considered as a life redeemed and provided by Christ, it is full of eternal glory:
what is mankind that you are mindful of them,
human beings that you care for them?
You have made them a little lower than the angels
and crowned them with glory and honor. (Psalm 8).
That is why we can both live and work for the Lord of glory because we know that nothing that is done in and for him, is ever useless, meaningless, or in vain.
Dale