Simon is an old friend of Daniel's, but they have not seen each other in years. When Simon meets Daniel again, Daniel is living with Rosh and the bandits on the hill; Daniel is consumed by his anger and driven by revenge, and Simon is worried about him. Simon explains how he feels about Rosh:
"...Rosh and I don't see eye to eye. For one thing, I prefer to earn my own bread and meat. [...] There will be need for warriors. But just now there is always a need for a good blacksmith."
(Speare, The Bronze Bow, Google Books)
In other words, Simon regards theft from innocents, even for the cause to which he is committed, as immoral. While Rosh claims to be working towards the building of an army to take Israel back, it turns out that he is actually simply stealing for himself. He doesn't actually care about Daniel or the cause, but uses it as a buzzword to manipulate people into working for him and ignoring his thievery. Simon, in contrast, actually cares about the cause for its own sake, and later, when he becomes an acolyte of Jesus, it can be seen that he is still working towards the cause but in peaceful terms. While Rosh claims to be working towards the cause in violence, Simon works towards the cause through speech and deed, changing hearts and minds. As shown above, Simon knows that his zealotry will be useless if he is killed in pursuit of the cause; instead, he remains alive and changes minds from within.