Pastoral refers to the countryside, particularly an idealized view of the country. If you draw cheery pictures with lush grassy fields, calm skies, a farm animal or two, and some flowers, you draw pastoral scenes.
Pastoral can also mean something done by, you guessed it, a pastor. If a pastor writes a letter to his congregation, it is a pastoral letter. How are they related? Shepherds, of course. Pastors are often referred to as shepherds of their flock (i.e., the members of their church congregation). Actual shepherds, the kind who tend sheep, work in pastoral settings.