For Plotinus, what really exists are the Platonic forms, so the true nature or form of things like justice, beauty, maybe numbers, things like that, and these he associates with the intellect because they're the objects of intellect, they are things that intellect can think about.

The importance of Plotinus is not only his own philosophical ideas which are quite interesting, but his historical impact as the founder of neo-Platonism which is the main philosophical tradition of late antiquity.

In fact Plotinus does believe in divine providence, though when he talks about divine providence, he talks about that providence being exercised by the intellect and the soul of the world, rather than the One.

What the soul is doing is kind of walking through the forms, and so our experience of thinking isn't normally this kind of pure intuitive insight that intellect gets, and that intellect must get right, because it's always identical to its objects, it's always the same as the forms that it's thinking about.

This is in a way the most important thing about soul is that it's a kind of principle which mediates between the universal intellect and the material world.

I'm sure that Plotinus wasn't that impressed by the Christians.

Plotinus is usually called the Founder of Neo Platonism and what that means is that in this philosophical circle, he was founding a kind of renewed attempt to understand the thought of Plato which however they were combining with the thought of other philosophers, including Aristotle, the Stoics and Pythagoreans and so on.