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.

When you're seeking after bodily pleasure of food and drink for example, this is going to prevent you from doing what you should be doing which is contemplating.

The idea is that to grasp an idea like equality or justice, you can't look at the equal and just or unjust things in the world around you, you have to somehow ascend to or maybe remember some kind of idea of equality and justice and this would be a Platonic form, and it would be different from the things that partake in the form.

Just the way you might look at a painting and see the painting, and the painting is outside you, so this immaterial intellect would see the forms and behold them, as if they were standing before it. And Plotinus said that that can't be right because it falls prey to sceptical objections.

The world around you is some kind of distraction at best, and evil at worst, and you should be turning away from it.

In fact one of the things about Plotinus is that he maybe not singlehandedly, but I think more than anyone else, killed off the variety and dissension among the philosophical schools of antiquity.

Assuming there is an intellect, we're clearly not this universal intellect or we would know it. So that's one function of soul.