The first line of the poem sounds like the start of a race: "Take your mark, get set, GO!" vs. "At the round earth's imagined corners, BLOW!" Clearly Donne could not have intended this parallel, but that verb hanging at the end of the first line does set off a frenzy of linguistic energy. The first line carries over into the second without a pause. The technical term for this is enjambment. Holy Sonnet 7 has a lot of enjambment, and if you heard it aloud, you wouldn't know where the lines start and end.
The speaker doesn't actually have the power to start Judgment Day, but he acts like a cheerleader at a race, urging the dead souls to "arise! arise!" and to "go!" to their scattered bodies.
Then the poem pivots on the word "but." At this point, the speaker starts making excuses, and the sound of the poem becomes more dense and legalistic. The whole sonnet is filled with commas and pauses, but after the word "space" in line 9, there is a larger pause, as if the speaker were doubled-over and winded. Having bought himself a moment or two, our speaker tries to justify calling off Judgment Day. At the end, the poem begins to sound more like an official plea to a powerful person, like the "pardon" it describes in the last line.