Nemesius of Emesa is a bit of a mysterious figure, so obscure in fact that the latest translation of the only book of his we have ('On Human Nature') has been translated recently by a medical historian rather than a theologian. He was writing in the late 4th century, around the same time as the more famous Gregory of Nyssa (honestly, he really is quite well known in the world of patristics). He's interesting because, unlike a lot of his contemporaries, he seems to have been pretty hot on the classical philosophers and thinkers from Plato and Aristotle to Galen (a big medical man) rather than just having read about them second hand.
Nemesius claims to be the Bishop of Emesa, which we have no reason to disbelieve. Emesa was one of the more hellenised (that is, Greek culture-ified) parts of Syria, so he may well have had a proper classical education. Although he wrote in the fourth century, no one seems to have heard of him until the 7th century, when first Maximus the Confessor wholesale lifted bits of his writing and incorporated them into his work (he wasn't a big one for quoting his sources, which was more ok then than it is now), and then John of Damascus both quoted and acknowledged him. He later became popular in 'floria legia', which are big books of quotations from the Fathers which were used in Byzantine monasteries to educate monks, functioning a bit like the wikipedia of their day: want to know about the incarnation? Read this bit from Father X, he's good.
The reason that Nemesius got popular in these compilations is that he had a very neat solution to a very vexing problem. Given that humans are able to choose to repent, or to sin once they've been righteous for a bit, what's to say that the angels and demons can't similarly recant and swap places? No one really wanted to allow for this possibility, because it causes all sorts of celestial chaos: bad enough keeping tabs on flighty humans, let alone a whole cosmos of beings switching allegiances and changing their mind, and heaven forbid we have to start seeing even Satan as capable of repentance.
But how do you explain the difference between humans and the spiritual beings? The problem was made worse by Origen, who occupies an interesting place between respected Father of the Church and heretic. On the one hand, he came up with some important and influential theological ideas; on the other, he thought that the cosmos had started out with loads of beings, all of whom had fallen. The ones who fell a lot and were really naughty were made into demons; the ones who hardly screwed up at all became angels, and the middling sinners became human beings. Odd, no?
How to get away from Origen, then? Nemesius did it by arguing that the thing that's distinctive about human beings is that they have both souls and bodies. Animals and plants have bodies but no souls; angels and demons have souls but no bodies. This uniquely human combination gives humans two special privileges. On the one hand, only humans are pardoned when they repent; on the other, they're the only bodies to be granted eternal life. The pardoning privilege comes from the body, because unlike the angels and demons, human beings have animal needs and affections which can lead them astray. The bodily immortality privilege comes from the soul, which is immortal and thus grants immortality to the body.
This is a very satisfying theological solution, because it's often difficult for the Fathers to give the body much significance - they tend to see the soul as more important and generally better, and so often drift away from orthodox Christianity which demands the redemption and resurrection of the body. It also, I think, plays nicely into a lot of contemporary discussions about the future destiny of the physical creation, which has implications both for Christian environmental ethics, and also for our attitude to work. Whether it solves the problematic questions about the potential salvation of the devils which arise from the discussion of evil as deprivation, though, I'm less sure...