In “mending wall,” what does the imagery of “and set the wall between us once again” mean?

What is a brief and often humorous statement of truth or opinion such as a watched pot never boils

In shakespeare’s hamlet what word can be substituted for allusion in the phrase the illusion is that not only does larry us die as expected but hamlet is doomed to die by the poison on his own sword as

Laugh and be merry, remember, better the world with a song,    better the world with a blow in the teeth of a wrong.    laugh, for the time is brief, a thread the length of a span.    laugh and be proud to belong to the old proud pageant of man. (laugh and be merry/john masefield/public domain) which of these is the main idea of the poem?