Let us now examine how it happens that the soul descends into the body, and in what manner this occurs; for it is sufficiently astonishing and remarkable. For a soul, there are two kinds of entrance into a body. The first occurs when the soul, already dwelling in a body, undergoes a transmigration; that is, passes from an AERIAL or igneous body into a terrestrial body. This is not usually called a transmigration, because the condition from which the soul comes is not visible. The other kind occurs when the soul passes from an incorporeal condition into any kind of a body, and thus for the first time enters into relations with a body. (Ennead IV,3 (27) 9)
How do Guardians participate in matter, and of what matter are they formed? This their matter is not corporeal, otherwise they would be animals with sensation. In fact, whether they have AERIAL or fire-like bodies, they must have had a nature primitively different (from pure Intelligence) to have ultimately united each with his own body, for that which is entirely pure could not have immediately united with a body, although many philosophers think that the being of every Guardian, as guardian, is united to an air-like or fire-like body. But why is the being of every Guardian mingled with a body, while the being of every deity is pure, unless in the first case there be a cause which produces the mingling (with matter)? This cause must be the existence of an intelligible matter, so that whatever participates in it might, by its means, come to unite with sense-matter. (Ennead III,5 (50) 6)