
The “sins” of First Cov have been obscured by distortions and omissions. Basically, the denomination wants uniformity as opposed to a fundamental concept, i.e., congregationalism, adopted by its founders. Because First Cov. envisioned having a same-sex marriage in its building at some point in the future (and there are other “reasons”), the denomination not only kicked out the church, but also revoked the ordination of its lead pastor for supporting same-sex marriage. The denomination also revoked the ordination of a retired pastor who presided over the same-sex wedding of his son.
Here’s some reading material, starting with an academic approach.
https://pietistschoolman.files.wordpress.com/2019/06/covenant-harmony-and-liberty-1.pdf
The denomination has stuff on its website. Scroll down to the right.