I bought The Complete English Works of George Herbert recently, hoping to add a little more poetry and devotion to my reading list. Not 10 minutes after laying my hands on it I read "Bitter-sweet" and knew I would not be disappointed. I'm tempted to say these are the best 8 lines of English poetry I know of.
Bitter-sweet
Ah, my dear angry Lord,
Since thou dost love, yet strike;
Cast down, yet help afford;
Sure I will do the like.I will complain, yet praise;
I will bewail, approve;
And all my sour-sweet days
I will lament and love.
(I've also discovered that John Piper quotes this poem in When the Darkness Will Not Lift (PDF), pg. 78.)