What is a key poem by george herbert?

"All of Herbert's English surviving poems are religious, and some have been used as hymns" (George Herbert - Wikipedia, the free encyclopedia). Go to your public library to get (or interlibrary loan) G. Herbert, The Works of George Herbert, ed. F. E. Hutchinson, 1945.
G. Herbert, The English Poems of George Herbert, ed. Helen Wilcox (Cambridge University Press, 2007).