Christianity is like the world. The world is more than 200 nations who all hate each others' guts. They are all lead by more or less corrupt governments who use their people's fear and hatred of outsiders to legitimize their claims to rule. So also Christendom is broken up into hundreds of churches, denominations, congregations, etc. each claiming to be the One True Church founded by Christ Himself, and that all the others are frauds of the devil. Despite all the diplomatic bloviating every few decades about "ecumenism" and "dialogue," these churches aren't really interested in talking to each other at all. They are all interested in exterminating their competition. Each one claims the Key to the Kingdom, and each expects to be sitting at the Right Hand of God laughing at all their competitors going down the gullet of hell in the end times. Like everything else in the world, Christianity is about winning. Maybe that's what folks mean by "muscular Christianity."
I've always liked Paul Tillich's thought that the absolute worst thing we could say about Jesus is that He came into the world to found a new religion. He did no such thing. He came into the world to end religion. That burden He promises to lift from our shoulders is not the burden of life, but the burden of religion; no more purity codes, no more tests and initiations, no more sacrificial regulations, no more chosen priesthoods, no more doctrinal purity tests, no more catechism pop quizes, no more law codes, no more celestial jurisprudence, no more moral or spiritual supremacy, no more apotheoses, no more holy heroism. All that is required for salvation has already been done for us. No matter how brilliant or base we are, it doesn't matter. We are all equally beneficiaries.