Sometimes clichés are true.

Before the 3rd century you're having several philosophical schools still as a going concern. You have not only the Platonists and the Aristotelians but you have Scepticism, you have Stoicism, you even have a little bit of Epicureanism. And what happens after Plotinus is that everybody becomes a Neo-Platonist. So if we then go forward to the Islamic world for example, Plotinus is immensely influential, and Neo-Platonism becomes at least one major component of mainstream Islamic philosophy as well.

In fact Plotinus thought not only that soul in general is eternal so that you always have soul, but he thought that each person's soul is eternal.

The intellect must be different from the soul.

The forms in intellect are some kind of blueprint or model on which the physical world is based, and something needs to come along and shape the matter in accordance with that blueprint. What does that is soul.

Basically the problem is that if the intellect is looking at or beholding the forms, what it will get is some kind of representation or image of the forms, but it won't actually have the forms, it won't touch them as it were, or it won't incorporate them.

The soul must be distinct from intellect because even at its best, what the soul does when it's thinking, is it thinks linguistically, it thinks in a temporarily extended way, so it for example, might go through the steps of an argument chain, as if you were going through a syllogism and seeing that something followed from the premises, whereas intellect simply grasps the forms.