A smile because the nights are short!
 And every morning brings such pleasure
Of sweet love-making, harmless sport:
 Love that makes and finds its treasure;
 Love, treasure without measure.
A sigh because the days are long!
 Long, long these days that pass in sighing,
A burden saddens every song:
 While time lags which should be flying,
The first line of the second stanza echoes the first, including the exclamation mark, but is of course inverted. The “smile” is now a “sigh”, and “short” days are now “long”. These  binary opposites  are the essence of the poem.
A Smile And A Sigh