So who is Jacob? Everyone wants to know. Everyone has an opinion. A few things are mostly agreed upon: he is a smart and handsome young man, and no doubt up to something, and prone to boating naked, and this in proper, pre-World War I England.
The story is like following Jacob around a rambling old house in the shoes of this or that observer(a friend, associate, aunt, lover), the rooms being this or that time, place and encounter,commencing in his childhood, proceeding through college and his travels abroad, ending with his death in the war. We are left with only a scattering of personal artifacts in his empty room, about which to continue speculating.
Occasionally we glimpse Jacob's perspective but are never allowed more than glimpses, and that is the point. No matter how intrigued we may be by another, or how compelling he seems, we are chasing shadows because:
"Life is a procession of shadows, and God knows why it is that we embrace them so eagerly, and see them depart with such anguish, being shadows. And why, if this and much more than this is true, why are we yet surprised in the window corner by a sudden vision that the young man in the chair is of all things in the world the most real, the most solid . . . for we know nothing about him. Such is the manner of our seeing. Such the conditions of our love . . . But something is always impelling one to him vibrating, like the hawk moth, at the mouth of the cavern of mystery, endowing Jacob Flanders with all sorts of qualities he had not at all -- for though, certainly, he sat talking to Bonamy, half of what he said was too dull to repeat, much unintelligible, and what remains is mostly a matter of guesswork. Yet over him we hang vibrating."
In that passage you can hear the author interjecting herself. This and other narrative devices made the book experimental for its time. I'm told it's an important read for that reason, but I have yet to read anything by Virginia Woolf that is not worth reading for the language alone.