Ahh, this line is a breath of fresh air. The natural word can’t be used up (or "spent").
"Spent" also connects this line to line six (think "trade"). In addition to meaning "used up," spent is also what continually happens to our money, sometimes before we even get it.
The speaker seems to believe that no amount of dirty "trade" can truly hurt "nature." The natural world can "never" really be traded, not for money or anything else.
Nature, as a work of God, is beyond all this.
This is a relief to hear, but seems to contradict the previous lines where it was suggested that everything is very temporary.
This departure could be a change in the way the speaker is looking at things. It could also signal something more complicated, like the idea that nature is both eternal (because it’s "charged with the Grandeur of God") and temporary, because the planet is temporary.
This line makes us feel as if the speaker has been traveling through a bleak and polluted city and has finally arrived in a land unspoiled by human intervention.
There lives the dearest freshness deep down things;
This train of thought continues, in what we think is one of the loveliest lines in all of poetry.
In nature, the lines says, all the sweetest, cleanest, things are living.
In the previous stanza the speaker laments what people have done to the world. In this stanza, the speaker has now discovered that below the surface nature thrives.
This idea also meshes well with the earlier concept that the earth is seared and calloused on the surface.
What a refreshing drink of cool water these first few lines are, after all that harsh images of the first stanza.
And though the last lights off the black West went Oh, morning, at the brown brink eastward, springs--
This is a fancy way of saying, even though the sun sets in the west, and the night comes, morning always follows, with moving lights and fresh energy with the rising sun in the east.
This line reminds us of the title of a famous work by a man who came before Hopkins, St. John of the Cross. This Saint John (not to be confused with other Saint Johns), was a Roman Catholic mystic and a poet. His work is called The Dark Night of the Soul, and is about the struggle to find light in the darkness of existence.
Because the Holy Ghost over the bent World broods with warm breast and with ah! bright wings.
On the most basic level, the final lines state that daylight continues to follow night, "because" the Holy Ghost is hovering over the world, disturbed, but warm and benevolent.
We can take it even deeper.
The Holy Ghost (also known as the Holy Spirit) was said to be seen in the form of a dove at the baptism of Jesus.
In Christian theology, the Holy Ghost is part of the Holy Trinity, which also includes God and Jesus (the Father, Son, and the Holy Ghost).
The dove imagery is enhanced by the word "broods," which has a gloomy, moody sound to it.
On the one hand to brood is to think deeply about something perplexing.
On the other hand, a mother bird broods when she sits on her nest, helping her eggs get ready to hatch.
The poem’s ending suggests that the world is in embryo, so to speak, yet to be completely born.
The shell of the egg connects with the idea of a hard surface coating the earth, hiding nature beneath it, which we saw in lines five through seven.
Yet, here in the conclusion, this is seen in a more positive light. Think of the speaker’s confusing statement in line three: "it gathers to a greatness." Doesn’t an unborn chick gather to a greatness, as it prepares to be born?
Yet, the speaker also says that the world is temporary, like a flash of lightening.
This suggests that the "rebirth" of the world we see in the final stanza is just one step in the ultimate destiny of the word.
Still, the poem ends on a fresh, happy, perhaps even comforting note. It even has an "ah" and an exclamation point!
One more thing: next time it’s cloudy, look up at the sky and think of this poem. The cloud formations may remind you of the ending to "God’s Grandeur"?