Complex sentence: Matt Barnhart, a former Trinity Baptist Church member who had witnessed Anderson's "church discipline" session in 1997, had reported the session on a blog (Independent Fundamentalist Baptist (IFB) cult survivors).
Split into simpler sentences: Matt Barnhart, a former Trinity Baptist Church member, witnessed Anderson's "church discipline" session in 1997. Barnhart had reported the church discipline session on a blog (Independent Fundamentalist Baptist (IFB) cult survivors).