Surface response: under no circumstances should anyone be obligated to read that book (or any religious text that I know of).

Deeper response: you made a foolish promise. Skimming the thread, I conclude that you escaped, this time. Your interlocutor hardly confronted your characterization of his "evidence"; he or she just dug up more cached apologia.

I'd have recommended breaking your commitment if I'd judged you'd failed, so I have no ulterior motive.