But why did Jews persecute Christians? Were they not both in the same boat -- branded as atheists, regarded as the scum of the earth, scorned when doing badly and resented when doing well? The answer here clearly lies in the ferocity of polemic between different pressure-groups, parties and/or sects within the same parent body. Sibling rivalry is fiercest when the siblings have an inheritance to share, or when one feels that another is ruining the chances of any of them inheriting it at all.

bishop n.t. wright, new testament and the people of God, p.450

interesting. also why i think it likely that islam arose out of arian/jacobite heresy and is not simply a different religion than Christianity.