I'm not going to write about the entire book right now, but simply focus on one chapter.
[4:1] What causes quarrels and what causes fights among you? Is it not this, that your passions are at war within you?  You desire and do not have, so you murder. You covet and cannot obtain, so you fight and quarrel. You do not have, because you do not ask.  You ask and do not receive, because you ask wrongly, to spend it on your passions.  You adulterous people! Do you not know that friendship with the world is enmity with God? Therefore whoever wishes to be a friend of the world makes himself an enemy of God.  Or do you suppose it is to no purpose that the Scripture says, “He yearns jealously over the spirit that he has made to dwell in us”?  But he gives more grace. Therefore it says, “God opposes the proud, but gives grace to the humble.”  Submit yourselves therefore to God. Resist the devil, and he will flee from you.  Draw near to God, and he will draw near to you. Cleanse your hands, you sinners, and purify your hearts, you double-minded.  Be wretched and mourn and weep. Let your laughter be turned to mourning and your joy to gloom.  Humble yourselves before the Lord, and he will exalt you.
 Do not speak evil against one another, brothers. The one who speaks against a brother or judges his brother, speaks evil against the law and judges the law. But if you judge the law, you are not a doer of the law but a judge.  There is only one lawgiver and judge, he who is able to save and to destroy. But who are you to judge your neighbor?(James 4:1-12 ESV)
I have always viewed the fourth chapter of James as a rebuke and an exhortation. What's causing all the fights among you children, I'd ask. Don't you know it's because of your passions that war within you? I'd tell the kids to examine themselves and realize they had the wrong focus. I'd use the chapter to rebuke them for fighting, and tell them to humble themselves and smarten up.
But I was missing the point.
It's all about LOVE.
Look at Verse 5:
Or do you suppose it is to no purpose that the Scripture says, “He yearns jealously over the spirit that he has made to dwell in us”?
Why are you fighting? You're not getting what you want, because you want to serve yourself. You desire something. You covet something else. You've got a friendship with the world instead of a deep, close personal relationship with God. You turn your back on the One who is everything, so you make yourself His enemy.
And yet, He yearns for you. He yearns jealously over the spirit that He has made to dwell in us.
This is not a petty, human jealousy. God has graciously placed HIMSELF into His children. In the new covenant (oh glorious thought!) He promised to dwell with us; He promised that He would be our God, and we would be His people. He promised to take out our hearts of stone and give us a heart of flesh. He wants to be everything to us. He wants His children to yearn for Him the way He yearns for us.
ESV Notes: God created mankind with a “spirit,” and he deeply desires that our spirits worship him.
The very next verse is "He gives more grace." He gives grace to His children, so we can love Him more than the "goodies" He bestows on us. If we love Him the way we ought to, we will not quarrel and fight, because we'll understand that every good and perfect gift is from our Father's gracious hand, and that He withholds no good thing from those who walk uprightly. He wants us to rest in His love, and be content with what we have.
If we love Him the way we ought to, we'll resist the devil and all his worldly temptations, and flee to God. We'll cleanse ourselves and purify our hearts by weeping and mourning over our sin. We won't speak evil of our neighbour, but trust God to bless or exact vengeance if need be. Shall not the Judge of all the earth do right?
When we love our God wholeheartedly (because He first loved us), we won't plan our lives without thought of what God would have us to do.
 Come now, you who say, “Today or tomorrow we will go into such and such a town and spend a year there and trade and make a profit”—  yet you do not know what tomorrow will bring. What is your life? For you are a mist that appears for a little time and then vanishes.  Instead you ought to say, “If the Lord wills, we will live and do this or that.”  As it is, you boast in your arrogance. All such boasting is evil.  So whoever knows the right thing to do and fails to do it, for him it is sin. (James 4:13-17 ESV)
If we understand how great the love of God is towards us, we won't need to quarrel and fight.
He yearns jealously for the spirit HE has made to dwell in you. He loves you.
There's nothing else to do but to live for Him.