Among monotheistic world religions the concept of union with God is peculiar. World religions depend on the ineffability of God, his distance, in order to maintain his character as one who should be feared and followed. This has a dramatic effect on human ethics. If you are not in union with God then it makes sense that your behavior is only skin deep, it is outer devotion, it is performance-based. In Christianity God is connected to us at a deeper level. He is affected by us and, more importantly, we are affected by Him. This is why Christianity can, without being arrogant, unloving, or judgmental, talk about your sexual ethics and how we spend our money and our race relations and the need to forgive our enemies - because something greater than simple affiliation with God is at work here - we are in union with Him through faith in Jesus Christ. We belong to God, and the affection, blessing, love, commitment that rests on us also changes us. Union does not just challenge my behavior, it challenges my hope. It believes better than my belief, bringing me encouragement in my grief and repentance in my pride and perseverance in my parenting and fruitful living when I feel cold-hearted. An ineffable, distant God cannot do this. He or she or it cannot be in relationship with us; the argument James makes is that in the case of a moralistic or surface faith the heart of speech is unaffected, so our speech is unaffected.
If we are in union with Christ then speech is only one of the things that will be different in the world around us. We will be in union with the mission of Christ in the world, taking it upon ourselves to be Christs, to speak - and not just to speak but to live - in such a way that the world is rescued. We will not only be a people of the good news, but good news people; indistinguishable from the truth we bring.
In Christ you are willing to suffer for the other because they are you, they are your flesh. Christianity, union with Christ, gives the only rationale for true brotherhood and sisterhood, true unity in the world is born with unity in the Body of Christ, among the people of God. This is why a church consumed by spiritual maintanence, faith only, is so abhorrent to James, and we must continue to reject it and to push on as a church to something greater. Our union with Christ must bless the world. Our neighbor must reap the benefit or it isn’t union with Christ. The world is not civil, it is not safe, people do stupid, terrible, nonsense things to one another. The church must be uniquely courageous here because we have jurisdiction. Human identity is the image of Christ. Human flourishing is the Kingdom of Christ. This is our circus, these are our monkeys.