This poem by John Masefield is optimistic in tone and incredibly straightforward and hopeful in its subject. It seems to be a poetic expansion on the idiomatic saying "eat, drink and be merry, for tomorrow we die," which is itself a paraphrase of various verses from the Bible. The idea that our time is brief, and that we should therefore enjoy ourselves with friends while we can, is one to which many poets and philosophers have returned, as Masefield does here.
In the first stanza, he urges the reader to be merry and fill the world with song, in the knowledge that time is "brief" and we should be proud to have been allowed to be part of mankind, even for a brief space. Masefield continues the idea of life as a lighthearted and joyous thing by describing it as a "pageant," or spectacle.
In the second stanza, there is some gravitas in the reminder that the world was made by God, but made by God out of his own "joy." This being the case, the earth and everything in it are receptacles for God's "mirth," which Masefield imagines as wine from which we can drink.
In the next stanza, Masefield encourages us to drink from this cup, because it symbolizes the joy of God. He suggests that God wanted us to partake of this joy, so there is no sense in abstaining from it. Instead, we should laugh, "and battle, and work," and drink God's joy from the world around us.
The final stanza of the poem imagines the people of the world gathered in an "inn" together, indulging in merriment until "the dancing stops." Again, life is imagined here as first dancing, and then as a "game," rather than something serious to be toiled through. Masefield urges the reader to laugh and be happy until life comes to an end.