I can't really find a meaning for this sentence: And I had thought his words idle.
Idle words are meaningless words. Words that are spoken that mean/come to/amount to nothing.
As a car's motor is idle (out of gear), so too 'idle words' (words that are spoken, that are just noise) .
"And I had though his words idle" : I had thought his words were nothing important, (just idle chatter, idle talk, ) but he was actually saying something important/meaningful.