The tide rises, the tide falls,
The twilight darkens, the curlew calls;
Along the sea-sands damp and brown
The traveller hastens toward the town,
The tide rising and falling is a metaphor for life as a whole. It always continues the same routine, back and forth, day and night and it never stops. 
 Reading the poem out-loud, you can even hear the raising and lowering of your voice, giving the impression of “rising” and “falling”. 

The Tide Rises The Tide Falls