The early poetry of John Donne uses metaphysical conceits to show the physical union of the male and female, husband and wife, lover and mistress.
His complex use of conceits compares to the act of love to unusually intellectual areas: horticulture, alchemy, astronomy, navigation, military, law, and mathematics.
Overall, Donne focuses on the microcosm and macrocosm worlds of love. One act of love can save the world is a common theme in his poems. In "The Flea," for example, he wants society to leave he and his lover alone, and the poem's persona argues that the world is about to come to an end, so why not enjoy it. He turns the myth of sex (it was believed that the time spent having sex reduced one's life) on its head by saying that death by orgasm is worth it.
In "Valediction: Forbidding Mourning," Donne compares himself to the moving foot of a compass (his wife is the fixed foot), saying that if she remains planted (faithful) he will travel around her to form a circle, a symbol of perfect love (wedding band). This is a kind of sexist double standard: the wife should remain home while the husband travels, but it is clever in terms of geometry at least.