My role is not to administer the law, but obey it. We listen to God's word and apply it to those around us. But God wants to change me. James turns the horizontal matter of slander into a vertical matter of our relationship with God. James is not objecting to planning or profit, but to boasting about the future.
Boasting is about putting our confidence in something.
And the future is an unstable object of confidence. Time is not for proud achievement for self but for doing good for God. We don't know exactly who the rich were, but the Bible is first of all about God, not firstly about what we do. In the West we seem to be much softer about covetousness than sexual immorality. We watch greed on TV without even thinking about it.