Heinlein devotes a good deal of the narrative to sexuality, which the novel presents as a physical expression of love and spirituality and as an exercise of free will. Who copulates with whom on Harshaw’s property is neither questioned nor judged, as long as it’s kept between consenting adults and no one is harmed. When Smith finally engages in sexual intercourse for the first time—with whom is never revealed—he matures from nestling to adult overnight. Patricia is the personification of this intersection. Initially a devout Fosterite, she views sex not as dirty or shameful as so many religions preach, but as pleasurable and therefore good. Heinlein, a libertarian in his later years, sees no conflict between sex and religion, and Smith’s Church of All Worlds incorporates sexual engagement as one of its fundamental premises.

The Christian admonitions against sexual pleasure are partly rooted in the “secular philosophies that were prevalent during Christianity's formation” (Helminiak, Daniel. “Sex as a Spiritual Exercise.” Yale Divinity School, 2006). The Stoics of the time believed in a division between body and spirit, a division that sexual pleasure only exacerbated. Smith’s Martian philosophy argues that no such schism exists and that, mind, body, and spirit must coexist for humanity to reach enlightenment.