Because he is aware of practical problems in the community, James makes an abrupt switch from peacemakers, the wise leaders of the community, to the actual situation of intrachurch conflict.

4:1 What causes fights and quarrels among you? That is a good question, for if God’s wisdom is found in peacemakers, community strife does not come from them. A conflict with the pagan world or the synagogue might be the inevitable result of following Christian standards, but these are quarrels within the church (i.e., among you); civil war, not national defense.

James asks the question rhetorically, for he knows the answer: Don’t they come from your desires? As in 1:13–15, he will not blame external forces: the source is their own evil impulses or, as Paul would say, the old (or fleshly) nature. The…