What does Antolini's quote mean, (188) "The mark of the immature man is that he wants to die nobly for a cause, while the mark of the mature man is that he wants to live humbly for one"?

I think that Mr. Antoli is trying to tell Holden to not be so extreme and impulsive in his judgments and actions. Holden gravitates towards the extremes. He has ideals that he nor any adult can live up to. I think Mr. Antoli just wants Holden to tone things down a little.