In "Porphyria's Lover," Browning is addressing the obsession the outwardly polite and prudish Victorian society had with sensational stories of horror and depravity. The themes of sex and violence and madness in this dramatic monologue speak to this obsession.
Browning turns the conventional presentation of these issues and themes, however, by making them seem natural and beautiful. Porphyria glides (line 6) in amidst the rain and the wind and shuts out the cold and the storm (line 7). She builds a fire that warms the cottage (line 9). She bares her shoulder (line 17) and lays her hair upon his cheek (line 19).
At a poignant (a feeling of specialness) moment, she totally gives herself to her lover, and he, trying to preserve the moment, strangles her with her own hair, painlessly, according to the speaker.
Browning forces readers to contemplate the relationship between sex and violence and power and complex madness, as well as beauty.