In the realm of the Buddha’s enlightenment, everything should be basically equal; there cannot be any discrimination between better and worse. But the “hearers” and “private Buddhas” tend to distinguish their own personal enlightenment from that of Sakyamuni. Consequently, even if they do attain a certain enlightenment of their own, it is not the enlightenment of the Buddha. They do not become Buddhas themselves. Instead they are called arhats, perfected ones, and are set apart from the general run of humanity.
Introduction to the Lotus Sutra