Rosh is the bandit leader who lives on the hills and trains Daniel in war and physical strength. He is a pragmatic man, driven by self-interest, who does not see the value of fighting for any specific cause. To write a monologue from his perspective, seek out the passages in the book where he speaks, and imitate his diction and cadence. He usually keeps his emotions hidden, and has no concern for others. One of his longest speeches comes when Daniel robs but does not kill a wealthy man traveling:
"I know what's in your mind," he said gruffly. "It's better to do without killing when we can. But there's a flaw in you, boy, a soft streak. I've seen it over and over, these years. Like a bad streak in a piece of metal. Either you hammer it out, the way you'd hammer out a bubble, or you'll be no good to us. When the day comes there'll be no place for weakness."
(Speare, The Bronze Bow, Google Books)
His inner monologue might focus on tactics, or on the state of his men -- remember, although he does not care about their welfare, it is in his best interests to at least keep them healthy. He might also have hidden emotions regarding Daniel; he has raised Daniel from a young age and possibly sees part of himself reflected in the younger man. If so, he would be furious that Daniel has left, and blame it on everything but himself; after all, he is always right. There would also be scorn for the cause of Israeli freedom; all he really cares about is lining his own pockets with stolen wealth.