Francis Thompson - Envoy

Go, songs, for ended is our brief, sweet play;
Go, children of swift joy and tardy sorrow:
And some are sung, and that was yesterday,
And some unsung, and that may be to-morrow.

Go forth; and if it be o'er stony way,
Old joy can lend what newer grief must borrow:
And it was sweet, and that was yesterday,
And sweet is sweet, though purchas-ed with sorrow.

Go, songs, and come not back from your far way:
And if men ask you why ye smile and sorrow,
Tell them ye grieve, for your hearts know To-day,
Tell them ye smile, for your eyes know To-morrow.

Francis Thompson

http://www.poemhunter.com/poem/envoy-3/