I wanted to riff off of something that the Bayly brothers noted here.
When we say that something is of cardinal importance, we are leaning on the older Latin meaning of the source word, cardo, which meant door hinge. Human sexuality is of cardinal importance. It is a hinge upon which all turns.
It is not merely a hinge upon which “earthly human society” turns, leaving out the spiritually minded folks of the church. The church is the reinvention of human society. The church is Humanity 2.0. The church is growing up into the perfect man, who is Jesus Christ. The church is supposed to model for a confused world what a real human society is supposed to look like. The church is not supposed to be a mirror that reflects the confusions of Manhattan right back at it.
God made us male and female, and this is the image of God (Gen. 1:27). We cannot talk about men and women without talking about the triune God, Christ and the Church, and the whole point of the gospel. We cannot talk nonsense about men and women without talking nonsense about the triune God, Christ and the Church, and the whole point of the gospel.
The Bible expects us to be able to tell what elements of the law are of cardinal importance (Mark 12:29). The Bible expects us to be able to tell what elements of the gospel are of cardinal importance (1 Cor. 15:3). Certain things are “weightier matters,” and other things are not (Matt. 23:23). We are expected to be able to look at the creation order and see those things which are of cardinal importance. This is a test which the evangelical and Reformed world is currently failing.
Now our understanding of our culture wars makes us instantly think that sexual confusions and perversions are matters of the law — and most of us are not failing there, at that point. In that limited arena, such things certainly are violations of the law. The apostle Paul brings the laws about sexuality to bear in the early part of Romans, as he is laying the groundwork for the gospel. God will judge men and women for their sexual perversity, and He will do so in accordance with His law. Of course.
But nobody thinks that Tim Keller is attacking the law. This, given his position, is actually more serious (and more subtle) than that. He is murking up the gospel. Given what marriage is created to declare (Eph. 5:32), sexual confusions are necessarily gospel confusions.
What do the homos of Manhattan need? They need Jesus, they need the blood of Jesus, they need the gospel, they need the one who brings them to the Father in the power of the Holy Spirit. They need the Trinity. They need to see the image of God as God displayed it — male and female created He them. They need to see the image of God as He redisplayed it in the gospel — Christ and the Church established He them.
And what is the cardinal weapon that in our day is being deployed against the gospel of triune grace? It is sexual confusion. It is sexual brinksmanship. It is sexual accommodation. It is sexual grammar parsing. And whatever else it is, it is now upon us.