Here is the past and all its inhabitants miraculously sealed as in a magic tank; all we have to do is to look and to listen and to look and soon the little figures—for they are rather under life size—will begin to move and to speak, and as they move we shall arrange them in all sorts of patterns of which they were ignorant, for they thought when they were alive that they could go where they liked; and as they speak we shall read into their sayings all kinds of meanings which never struck them, for they believed when they were alive that they said straight off whatever came into their heads. But once you are in a biography all is different. Source
What is meant by the "for" clause here? We arrange them in all sorts of patterns they were ignorant of because they thought they could go anywhere they liked? But it doesn't make any sense? I know overall it means we presume to know all kinds of things about the past and add interpretations of all kinds but it's far from reality. You will know it if you put yourself in a biography.
But it doesn't make sense here.
PS Is this "is" not supposed to be "are"?