God is not 'moved,' either by the suffering of the flower, or of humanity, in Emily Dickinson's poem 'Apparently with no surprise.' Although the poem seems to be superficially about one of her favorite themes - Nature - it can also be read as a discusion about the christian (particularly Roman Catholic) idea of Free Will. 'Why does God not help the oppressed and put an end to pain and suffering?' is a common cry. But many christians believe,as Emily Dickinson may have heard, that God allows his creatures (mankind) a free choice in the life he bestows upon them. If that leads to suffering or harm to others, he does not intervene. Like the Sun/son in the poem, he appears coldly unmoved - allowing Nature/events to take their course. to do anything else,some would say, would be to treat his creations like toys. Nevertheless, some may detect a bitterness or sadness about these lines - maybe Emily felt she did not have the full gamut of choices herself.
That's not much of a pun, but I guess it is one, sort of.
The whole point of the poem is that nature doesn't really care what happens to individual things, like one particular flower. The frost kills it, and the sun keeps on going and doesn't care that the flower died.
The pun is on the word "move." The sun moves (or appears to) across the sky. That's one meaning of move. But the other meaning of "move" is to affect something emotionally (as in "I was so moved by his speech that I cried..."). So the sun is moving across the sky but it is unmoved emotionally by the death of the flower. And that is a pun...