In Chapter 23, we finally meet the man responsible for the narrator's training. Brother Hambro turns out to be a tall lawyer who (no surprise here) thinks in incredibly macroscopic terms. He's the one to tell the narrator bluntly and repeatedly how "your members will have to be sacrificed."
For what purpose? We never learn. As might be expected of the person training new recruits, Brother Hambro is the mouthpiece of the Brotherhood's infuriatingly abstract theories.