When we had crossed the threshold of the door

Which the perverted love of souls disuses,

Because it makes the crooked way seem straight,

Re-echoing I heard it closed again;

And if I had turned back mine eyes upon it,

What for my failing had been fit excuse?

We mounted upward through a rifted rock,

Which undulated to this side and that,

Even as a wave receding and advancing.

“Here it behoves us use a little art,”

Began my Leader, “to adapt ourselves

Now here, now there, to the receding side.”