Proclus was the main channel of communication of late neo Platonism to Christianity. He emphasized the Platonic ideal of contemplative theology, developing it with a ritualistic element lacking before him. He had a three level structure for reality, like Plotinus, but these three were more like the Christian trinity interpenetrating, each one both an effect and a cause of the others.
He also re thinks the role of eros. For Plotinus, it can be interpreted simply as human need. For Proclus, it is a cosmic force.
Third, he describes the movement toward the One as a negation of negation. This will look familiar particularly to those who have studied Hegel. We cannot affirm things about God -- that "cuts off reality in slices", but does not give us the whole. Negations, therefore, are in order, but by themselves do not give us any positive identification. We only know the One in that it is not like other metaphysical beings. So, this negation has to be negated, to point to the One. Proclus is the first to make this move.
This negation is brought about psychologically. To attempt to name the One in this way is really to name our natural desire for the One, and thus direct us toward it (because of eros).
Proclus' influence on Christian mysticism comes mainly through Pseudo-Dionysius. Pseudo-Dionysius picks up the notion of cosmic love (eros), and also dialectical view of the One as negation of negation.