One of the largest obstacles to any biblical account of a pacifist ethic is dealing with the OT. Here I want to outline some methodological presuppositions as well as some hypotheses to be tested with regard to that obstacle:
1) The New Testament ‘trumps’ the Old.
Just as in many other regards the New Covenant supersedes the Old, fulfils it, transforms it, and so on, a NT ethic trumps the Old. In doing so, it must show continuity – for God does not change, and so must also show why things have changed.
2)‘Just’ violence is primarily about judgment – the destruction of sin and sinners
3) YHWH is a warrior – the emphatic note of the OT salvation-history with regards to Israelite conflict is that God fights for them. In response to that they are to trust in his deliverance, not in military might. Generally God involves and uses them in those conflicts, but not always.
4) OT themes of holy war are transformed, like many others, by a process of metaphorisation, into spiritual themes in the NT