To the Christian, the Other World was the Kingdom of Heaven, to be enjoyed after death; to the Platonist, it was the eternal world of ideas, the real world as opposed to that of illusory appearance. Christian theologians combined these points of view, and embodied much of the philosophy of Plotinus. [...] Plotinus, accordingly, is historically important as an influence in moulding the Christianity of the Middle Ages and of theology.
For several centuries after the Protestant Reformation, Neo-Platonism was condemned as a decadent and 'oriental' distortion of Platonism. In a famous 1929 essay, E. R. Dodds showed that key conceptions of Neo-Platonism could be traced from their origin in Plato's dialogues, through his immediate followers (e.g., Speusippus) and the Neo-Pythagoreans, to Plotinus and the Neo-Platonists. Thus Plotinus' philosophy was, he argued, 'not the starting-point of Neo-Platonism but its intellectual culmination.' Further research reinforced this view and by 1954 Merlan could say 'The present tendency is toward bridging rather than widening the gap separating Platonism from Neo-Platonism.'
Since the 1950s, the Tübingen School of Plato interpretation has argued that the so-called 'unwritten doctrines' of Plato debated by Aristotle and the Early Academy strongly resemble Plotinus's metaphysics. In this case, the Neo-Platonic reading of Plato would be, at least in this central area, historically justified. This implies that Neo-Platonism is less of an innovation than it appears without the recognition of Plato's unwritten doctrines. Advocates of the Tübingen School emphasize this advantage of their interpretation. They see Plotinus as advancing a tradition of thought begun by Plato himself. Plotinus's metaphysics, at least in broad outline, was therefore already familiar to the first generation of Plato's students. This confirms Plotinus' own view, for he considered himself not the Inventor of a system but the faithful interpreter of Plato's doctrines.
The joint influence of Advaitin and Neoplatonic ideas on Ralph Waldo Emerson was considered by Dale Riepe in 1967.
Neoplatonism and the ideas of Plotinus influenced medieval Islam as well, since the Sunni Abbasids fused Greek concepts into sponsored state texts, and found great influence amongst the Ismaili Shia. Persian Philosophers as well, such as Muhammad al-Nasafi and Abu Yaqub Sijistani. By the 11th century, Neoplatonism was adopted by the Fatimid state of Egypt, and taught by their da'i. Neoplatonism was brought to the Fatimid court by Hamid al-Din al-Kirmani, although his teachings differed from Nasafi and Sijistani, who were more aligned with original teachings of Plotinus. The teachings of Kirmani in turn influenced Philosophers such as Nasir Khusraw of Persia.
At least two modern conferences within Hellenic philosophy fields of study have been held in order to address what Plotinus stated in his tract Against the Gnostics and whom he was addressing it to, in order to separate and clarify the events and persons involved in the origin of the term "Gnostic". From the dialogue, it appears that the word had an origin in the Platonic and Hellenistic tradition long before the group calling themselves "Gnostics"—or the group covered under the modern term "Gnosticism"—ever appeared. It would seem that this shift from Platonic to Gnostic usage has led many people to confusion. The strategy of sectarians taking Greek terms from philosophical contexts and re-applying them to religious contexts was popular in Christianity, the Cult of Isis and other ancient religious contexts including Hermetic ones (see Alexander of Abonutichus for an example).
Plotinus offers a comprehensive description of his conception of a person who has achieved eudaimonia. “The perfect life” involves a man who commands reason and contemplation. (Enneads I.4.4) A happy person will not sway between happy and sad, as many of Plotinus’ contemporaries believed. Stoics, for Example, question the ability of someone to be happy (presupposing happiness is contemplation) if they are mentally incapacitated or even asleep. Plotinus disregards this claim, as the soul and true human do not sleep or even exist in time, nor will a living human who has achieved eudaimonia suddenly stop using its greatest, most authentic capacity just because of the body’s discomfort in the physical realm. “…The Proficient’s will is set always and only inward.” (Enneads I.4.11)