God created us in order that we would get along with one another. When sin entered the world, our fellowship with God was disrupted, of course, but so was our fellowship with one another. Adam and Eve hid from God after their sin, but they were also estranged from one another, which can be seen in how they blamed one another. And this has been the story of our race.
God in His grace redeemed us so that we would get along with one another. He called us out of our fragmented unbelief so that we could be one in Jesus Christ, that we would all speak the same thing, be likeminded, and confess with one mouth the gospel of God.
But the history of the Church thus far in some respects has been a melancholy one. This should not make us despair—God has promised us that the New Covenant will not end in exile for God’s covenant people as the Old Covenant did. The tree of the Lord will grow, and will fill the face of the world with fruit. But even though this is so, the New Covenant people have nonetheless done far more experimenting with little exiles than they should have done. We have done this by uniting with all the wrong people, and by dividing from all the wrong people. Whether driven by what was believed to have been high principle, or by grubby carnal motives, does not matter.
Where do wars and strife come from, James asks. He answers in two kinds—they come from internal lusts that are unmortified, and from external allegiances to the idolatries of the world. Take care—moderns are greatly confused about idolatry. Because we do not bow down to blocks of stone we think we are immune. But for centuries we have been burning little candles in front of our rationalistic constructs, and all in the name of sweet reason. Realize that these petty idols have no power (or desire, for that matter) to crucify your internal commotions.
So here is the command of God, in the name of Jesus Christ. You are the people of God, assembled in the name of His Son. Abandon every form of strife with one another. Be at peace.