The general case is that names in parentheses are maiden names.
However, it looks like the Barrington Congregational Church reverses maiden and married names. I have a couple sets of the membership list from that church and found the first attached image on the first page of that section.
I interpret the second sentence to say that the members are listed by the surname used when they joined the church. If a woman married later that name is included in parentheses. That would be the reverse of how we usually see, and key, them.
The second attached image is an example.
Do we just follow our usual keying guideline and hope those people will be found in a search or do we reverse our usual guideline for this church? (Or am I reading the introduction incorrectly?)