In chapter 3, James echoed Jesus, that out of the heart the mouth speaks (Matt. 12:34; cf. Proverbs 15:28). In order to tame the tongue (3:8), we need wisdom from above (3:17), that will change the jealousy and selfish ambition in our hearts (3:16). From these come every vile practice, but if they are transformed, then there will be peace between people (3:18).
That’s because these lusts are what cause quarrels and fights (4:1). James does not mean that good and bad passions are at war within the same person. Instead he means that when you see quarrels and fights between people - and he’s talking to Christians - you can assume they are being led by their “passions” - jealousy, and selfish ambition.
When we strongly desire what is not ours - coveting, the last commandment - but we cannot get it, we will quarrel with the person who does (4:2). This is how nations go to war, churches split, and marriages end.
This coveting and quarreling is a defection from God, a ceasing to trust Him as the generous, giving God. James calls this “adulterous” (4:4), a breaking of the first commandment, and making oneself an enemy with God.
Best then to get humble (6-10). Best to go back to Calvary, which reminds us afresh of how generous and giving this God is. No one is proud at the foot of the cross. God in His grace will take it from there.