The main thing to bear in mind is that the poem follows the movement of the year - it starts in the warmth of late summer, with bees, ripening fruit etc. Then in the second stanza comes harvest, with reaping and then gleaning (picking up the leftover corn etc after harvest.) In the third stanza winter is coming - the mood is darker and colder as the gnats 'wail' and the full-grown lambs (ie, nearly old enough to be slaughtered) bleat from the chilly hillsides. The poem ends with the swallows getting ready to migrate to warmer climates.
You can find more information from sparknotes www.sparknotes.com
You can find more information from sparknotes www.sparknotes.com