According to these texts, the sun god Ra passes through the underworld each night and unites with Osiris to emerge renewed, just as deceased souls do. However, the authors of a more recent commentary on Book 11 caution that the solar and underworld imagery could be based solely on Greek and Roman precedents, and they doubt Griffiths's assertion that Lucius undergoes a mystical union with Osiris. The "elements" that Lucius passes through in the first initiation may refer to the classical elements of earth, air, water, and fire that were believed to make up the world, or to regions of the cosmos. In either case, it indicates that Lucius's vision transports him beyond the human world. Panayotis Pachis suggests the word refers specifically to the planets in Hellenistic astrology. Astrological themes appeared in many other cults in the Roman Empire, including another mystery cult, dedicated to Mithras. In the Isis cult, astrological symbolism may have alluded to the belief that Isis governed the movements of the stars and thus the passage of time and the order of the cosmos, beliefs that Lucius refers to when praying to the goddess. However, in the course of the book, as Valentino Gasparini puts it, "Osiris explicitly snatches out of Isis's hands the role of Supreme Being" and replaces her as the focus of Lucius's devotion. Osiris's prominence in "The Golden Ass" is in keeping with other evidence about the Isis cult in Rome, which suggests that it adopted more themes and imagery from Egyptian funerary religion and gave increasing prominence to Osiris in the late 1st and early 2nd centuries CE. Gasparini argues that the shift in focus in the book reflects a belief that Osiris was the supreme being and Isis was an intermediary between him and humanity. This interpretation is found in the essay "On Isis and Osiris" by the first-century CE Greek author Plutarch, which analyzes the Osiris myth based on Plutarch's own Middle Platonist philosophy, and Gasparini suggests that Apuleius shared it. However, S. J. Harrison suggests that the sudden switch of focus from Isis to Osiris is simply a satire of grandiose claims of religious devotion. Because not all local cults of Isis held mystery rites, not all her devotees would have undergone initiation. Nevertheless, both Apuleius's story and Plutarch's "On Isis and Osiris" suggest that initiation was considered part of the larger process of joining the cult and dedicating oneself to the goddess.