Explain the structure of "God's Grandeur."

"God's Grandeur" is what's called a Petrarchan sonnet. This is a poem consisting of fourteen lines with a rhyme scheme of abbaabba cdcdcd. Petrarchan sonnets are divided into an octave (eight lines) and a sestet (six lines). The octave sets up a problem for which the sestet provides some kind of resolution.
In "God's Grandeur," the octet dwells on certain aspects of the ugliness of modern industrial Britain. God's grandeur is everywhere, yet modern man all too often ignores it. Hopkins wonders why men no longer "reck the rod," in other words why they don't show due reverence for Christ and his cross. Modern man is too busy defacing the land with his ceaseless toil to stop and wonder at the divine grandeur around him.
But in the sestet, Hopkins reminds us that, beneath all the man-made ugliness, nature is still deeply imbued with the spirit of its creator. This is an attempt to provide some kind of resolution to the problem established in the octave—contemporary man's disenchanted relationship to nature. However man may choose to regard the world around him, it will forever be "charged with the grandeur of God."
https://www.poetryfoundation.org/poems/44395/gods-grandeur