Like Rosh, Simon wants to see Israel liberated from the Roman occupier. Unlike the bandit leader, however, he believes that true liberation will only come from following in the footsteps of Jesus.
Rosh is very much in thrall to the prevailing notions of Jewish messianism, which hold that Israel will be liberated by a great warrior king, like David, who will drive out the Romans and free God's chosen people from their bondage. Until that day arrives, Rosh is determined to play his full part in the anti-Roman resistance movement, using whatever means necessary—no matter how bloody or violent—to achieve his aims.
For his part, Simon is staunchly opposed to violence. The way of Jesus is a peaceful one, and involves turning the other cheek. He conceives of liberation from the Romans mainly in spiritual (rather than political) terms. It is the inner freedom of the believer that he seeks, rather than the secular freedoms that come from Jews being able to run their own affairs. That's not to say that political freedom is completely unimportant to Simon, but his eyes are on a much bigger prize: the spiritual freedom of a Christian.