In these verses, James tells us that what causes fights and quarrels among us is that sinful desire in one or more of God's people is leading them into war with others among God's people. It is very hard to accept because it would mean that there is, in the midst of God's people, an active war being waged against God. As children of God, there is no reason that fighting and quarreling should ever go on among us. Let us follow his word into the fullness of unity that he desires for us.