A recent CTC comment:
"Sigh. Oh the extremes Protestants go to in order to justify their schism." [source]
This comment begin with the assumption that some group split from the Roman church, and Rome is the (or "a") true church. What happens if this assumption, that schismatic groups split from the true church, if it is denied that Rome is the (or "a") true church?
"In other words, it is not the children by physical descent who are God’s children, but it is the children of the promise who are regarded as Abraham’s offspring."