The Gospel Alliance’s distinctive that “the Church solemnizes a marital union between a man and a woman to reflect the covenantal love of Christ and His Church” is not calling for any sort of change in church teaching or practice, but rather reflects a desire for the church to stay in step with its historic and global teachings, as Preston Sprinkle so clearly discussed at the Gospel Alliance Gathering in his talk on Marital Union (see video of his talk here).
While some believe that a change in this doctrine would help the witness of the church moving forward, closer examination of churches that have changed their belief on this issue points the opposite way. Back in 2015, Time magazine featured a story about a large evangelical church in Nashville called GracePointe that changed its position on sexuality so that marriage was no longer viewed as exclusively between one man and one woman. As recently reported, since this announcement the church has seen a great decrease in size, with over half of its congregation leaving (many of their members and leaders seem to have left immediately). They are now selling their building to another church that holds to the historic teaching of the church concerning marriage and sexuality.
Deviating from the teaching that churches throughout time and across the world and theological spectrum have affirmed has not led to mission and multiplication, but rather division and decline. If we want to see the gospel move forward and change lives in our community and world, we need to be stay faithful to the teachings of Scripture that the church has held.