"Mostovskoy is in agony. He is now forced to admit to himself that he has had those doubts for a long time, that he hated his own party, the camps, the trials, Lubyanka, Ezhov, Beriya. ""By the end of the conversation the old revolutionary is broken. The psychological torture of being shown how his beloved party and ideology are in every respect the same as the party and the ideology of the hated mortal enemy, that in the enemy, as in a mirror, he hates himself and everything he believes in..."
Thanks Paul Bonneau.