The speaker sits in a dark room while a storm rages outside, and chooses to light up so they can see. Right away there's a small act of defiance: rather than hide from the weather, they stay alert to it. The storm is described as singing "a most excellent music," so the noise and violence of thunder and wind become something to enjoy, even admire.
The last couplet turns inward. The "blood I bleed out" suggests pain, and the speaker calls it "a dark pleasure." The inner storm seems to match the outer one. The title, "Sturm und drang," which means "storm and stress," points the same way, toward strong, turbulent emotion. The mood is intense but oddly calm: the speaker doesn't fight the suffering but takes a strange comfort in feeling it fully. Whether the bleeding is literal or figurative, the poem leaves us with a sense of someone finding energy, even satisfaction, in their own hurt.