SO basically I read some very interesting things. I'm so frustrated my super long message just got deleted and no I have to type it all over again :( :angry:.
Anyways I'll cut to the chase. I think he's talking about a previous life he had as a soldier and that when he says "prospekts how did I forget" he talks about himself now, and it surely must've been an important time of his previous life that he somehow recalled in this life. To support my point, I think that in the songs glass of water and violet hill the same PREautobiography comes back. In glass of water he talks about seeing an oracle and seeing the future. At a certain point when you can see your future i'm guessing you can see your past right. And I think that in violet hill he talks about his death as a soldier in the 19th century "falling down the house". I think all the songs that are related to this album talks about himself and what he was and what he is trying to discover. Well, all the other answers are in the song if you like for what he did in prospekts march. Plus in the first songs, some questions in " what if" engage this sort of theme. I'm sure he looked for a meaning, to clear all the doubts in his head and now has realised it. And in one of his prevoius lives he talks about him as a soldier in the albums VLVAADAAHF and propsekt's march. thanks for reading !!