To put a particular definition of marriage at the heart of the Gospel is to make a dangerous innovation on traditional Christian thought. To put a human construct in a place that only Christ has the right to occupy. The Gospel has never been a moral code, and has never been about anything human beings do. To replace that traditional idea of the Gospel with a moral code based on one particular (and arguable) interpretation of only a few passages of Scripture is, to my thinking, an offense against the Gospel, not a preservation of its witness.