When did he write this?

It is impossible to date this poem, and therefore all we
can do is surmise that it may have been inspired by the occasion of a trip, upon which
the poet found a need to answer objections that might have been raised to his going.
Readers brought up in the twenty-first century may wonder why a trip should be a cause
of consternation or grief. Readers might need reminding that even a short trip in the
days of horse and sail would require an absence of at least several weeks, and perhaps
several months. More to the point here is the extensive use of metaphorical language,
together with the universally famous concluding metaphysical conceit, or simile, about
the relationship of lovers to a geometric compass. It is of course important to explore
this simile in some detail, for whenever students of literature refer to the
“metaphysical conceit” they invariably turn to this poem and this
comparison.