First, the poem:
We travelers, walking to the sun, can’t see
Ahead, but looking back the very light
That blinded us shows us the way we came,
Along which blessings now appear, risen
As from sightlessness to sight, and we,
By blessing brightly lit, keep going toward
That blessed light that yet to us is dark.
Wendell Berry, Given: New Poems (Berkeley, CA: Shoemaker Hoard, 2005), 74.
And here is the sermon.