This from Robert Browning (everyone knows the first part):

If a man’s reach does not exceed his grasp, what is heaven for?

And this:

Browning was teaching a class one day and a woman raised her hand.  “Professor Browning,” she said.  “I love your poetry and I have read all your poems.  There is one line, however, I just don’t understand.”  She quoted the line.  “Can you tell me what you meant?”

Browning considered the question for a moment.  Then he said, “You know, when I wrote that line only God and I knew what it meant.”  He paused, then continued, “Now only God knows.”