When the soul has descended into generation (from its first divine condition) she partakes of evil, and is carried a great way into a state the opposite of her first purity and integrity, to be entirely merged in which, is nothing more than to fall into dark mire.
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The soul therefore dies as much as it is possible for the soul to die :and the death to her is while baptized or immersed in the present body, to descend into matter, and be wholly subjected by it; and after departing thence to lie there till it shall arise and turn its face away from the abhorrent filth. This is what is meant by the falling asleep in Hades, of those who have come there.
Γινομενῳ δε ἡ μεταληψις αυτου. Γιψνεται γαρ πανταπασιν εν τῳ της ανομοιοτητος τοπῳ, ενϑα δυς εις αυτην εις βορβορον σκοτεινον εσται πεσων.—Αποϑνησκει ουν, ως ψυχη αν ϑανοι· και ὁ ϑανατος αυτῃ, και ετι εν τω σωματι βεβαπτισμενη, εν ὑλῃ εστι καταδυναι, και πλησϑηναι αυτης. Και εξελϑουσης εκει κεισϑαι, εως αναδραμῃ και αφελῃ πως την οψιν εκ του βορβορου. Και τουτο εστι το εν ᾁδου ελϑοντα επικατα δαρϑειν.
Plotinus, Ennead I book viii