Simon is a zealot, working towards the cause of Israeli freedom. However, in contrast to Daniel, Simon's work is in knowledge and love, not in violence. Daniel wants revolution; Simon wants peace and acceptance of love. Jesus affects Simon much more strongly than Daniel, because Simon already accepts parts of his philosophy. When Jesus creates bread, the villagers are ready to crown him king, but Jesus refuses, and that is what makes Simon think that Jesus is the true Messiah.
"You've seen him caring for those people -- the ones so low that no one, not I or anyone else, cared what happened to them. When I see that, I know that the God of Israel has not forgotten us. Or why would He have sent Jesus to them, instead of to the rich and the learned? Like a shepherd, he says, who will not let any of his sheep be lost. I'm a poor man, and ignorant, but I know now that with a God like that I am safe."
(Speare, The Bronze Bow, Google Books)
It is the empathy and love of Jesus, not the violence and theft of Rosh, that is important to Simon. In Simon's eyes, a true God does not send destruction to enemies, but instead gives them the tools to change their own minds of their own free will. Jesus is one such tool. The miracles that Jesus performs, such as the bread and healing the sick, are simply earthly manifestations of God's love of all men. Simon accepts this along with the love he already feels and accepts Jesus as Messiah, while Daniel, still consumed by hate, takes much longer.