Board Thread:Warhammer 40k General Discussion/@comment-192.226.225.70-20131002223609/@comment-78.53.12.74-20150207222449

In order to understand this, one has to understand what Nurgle really stands for, which is not disease unlike most people's (superficial) perception of Nurgle, but despair. Disease causes despair, it is a means to an end, but disease is no emotion and ALL Chaos Gods are manifestations of emotions (you will easily know what the other big three Chaosgods stand for as they are less subtile).

Returning to your question as to why/how plague marines work: this is exactly the idea. A normal human being like you sees a rotting space marine and thinks he must be weak, slow, bad for combat in every respect. But if you were actually fighting against him, you would see the opposite. He would be faster than you, stronger than you, better coordinated, and a hell of a lot tougher than you. This is because the rotten appearance is Nurgle's way of mocking your expectations. Your initial thought upon seeing these warriors will be that they will be easily defeated, after all they are half dead already. Upon fighting them, you will see that the opposite is true, they are not weaker, but at least as strong as they were before the infections and even tougher now. Hence your hope will vanish and that is when Nurgle's favourite emotion comes into play: soldiers will despair and not understand how this can be true. Logic itself does not allow these half-zombies to be so strong, so fast, so intelligent, but it is all true and it is all meant to break morale and hope.

Sadly, GW has broken a little bit with lore in the most recent rules as they start depicting nurgle daemons and followers at least a little slower than their counterparts. If you look at older (more original) rules, you will see that plaguebringers were very fast (I think initiative 5? Which is unreal-speed from a human's eyes) and Plague Marines were just like Space Marines, just tougher.