Complex sentence: The phrase "rocking and rolling" originally described the movement of a ship on the ocean, but was used by the early twentieth century, both to describe the spiritual fervor of black church rituals and as a sexual analogy.
Split into simpler sentences: The phrase "rocking and rolling" was used by the early twentieth century as a euphemism for sexual intercourse. The term "rock & roll" later came to to describe the spiritual fervor of black church rituals and as a sexual analogy.