Historical Context in A Valediction: Forbidding Mourning
In the Petrarchan sonnet tradition, the speaker would often break his love object into her distinct parts in order to describe each one as perfect and beautiful. He would focus on her physical parts and compare them to greater concepts, such as her lips red as a rose. Here Donne uses a catalogue of human parts as an anti-blazon that pushes back against the Petrarchan tradition in order to declare that their love does not care about these physical markers (or this poetic representation of perfect love).
A dominant theory of astronomy from the 9th to 16th century stated that there were 9 hollow globes that moved around the Earth in elliptical circles. Trepidation was the oscillation, that is a change or variation in a sphere’s predictable movement. The speaker compares the movements of the earth, as in earthquakes, tidal waves, etc, to the movement of the “spheres” to show that while the movement of the spheres is colossally larger in scale, it causes less harm than movement on the Earth.
The speaker turns abruptly away from this scene to speak to his lover about their love. This movement of focus from death to life is reminiscent of Carpe Diem poetry in which the speaker reminds his love object and addressee of the immanence of death in an attempt to get her to appreciate the beauty and importance of their love.