What is the historical significance of Neoplatonism?
The main historical significance of Neoplatonism (outside of its significance for people who study the history of philosophy) is that it helped to influence the thinking of many Christian thinkers. The most important of these Christian thinkers was St. Augustine.
One of the major teachings of Neoplatonism was that everything must come from a being that is completely beyond the reach of human understanding. That being is so far beyond humanity, this holds, that any ideas that we can possibly have about it (through our rational minds or our imaginations) are simply wrong. We have to strip away all our conceptions of that being in order to uncover what is truly divine. Many early Christian thinkers adopted this idea as a way of understanding the Christian God.