To talk about the sound of Holy Sonnet 14, it's helpful to have a fancy word in tow: plosives. Plosives (think "explosive") are the kinds of sounds that we make by using something in our mouth (or lips) to stop the flow of air, and then suddenly release the air, making for an explosive sound. The letters t, k, p, d, g, and b are the basic plosives in English. These letters often have a hard, violent sound, when compared to, say, h or the vowels.
Now, take a look through the poem, and check out how often the speaker uses plosives. Check out line 4: "to break, blow, burn." That word "break" comes up again in line 13, when the speaker says, "Divorce me, untie, or break that knot again." Go ahead; say "break" out loud. Really. Hear how violent it is, both at the beginning and the end? Whenever the speaker is talking about how he wants God to treat him, the sonic quality of the language becomes violent and intense.
There's actually one cool exception: in the last line, when the speaker asks God to "ravish" him. That word there is interesting because its connotations are violent, but instead the speaker uses a softer, more whisper-like sound. It's almost as if, by the end of the poem, the speaker can be more intimate with God – instead of yelling, he whispers that second syllable of "ravish," savoring the idea.