What is the theme of this poem?

i hear america singing, the varied carols i hear;
those of mechanics--each one singing his, as it should be, blithe and strong;
the carpenter singing his, as he measures his plank or beam,
the mason singing his, as he makes ready for work, or leaves off work;
the boatman singing what belongs to him in his boat--the deckhand singing on the steamboat deck;
the shoemaker singing as he sits on his bench--the hatter singing as he stands;
the wood-cutter's song--the ploughboy's, on his way in the morning, or at the noon intermission, or at sundown;
the delicious singing of the mother--or of the young wife at work--or of the girl sewing or washing--each singing what belongs to her, and to none else;
the day what belongs to the day--at night, the party of young fellows, robust, friendly,
singing, with open mouths, their strong melodious songs.