If all baptized persons become adopted children of God are they than part of the body of Christ on this earth? Are they members of the Mystical Body of Christ or is that membership inclusive of only Catholics?
No one out there knows the answer? Or is it just a dumb question?
I would say yes, baptism makes them members of the mystical body of Christ (which is the Catholic church). As they grow up in other churches, they accept teachings which differ from Catholic doctrine (but not realizing the errors). So they become separated from us in belief. So we refer to them as our separated brethren but they are joined to us by their belief in Christ and by their baptism.
This doesn’t mean that there is an invisible ‘catholic’ church or that their erroneous beliefs are unimportant. But they are still joined to Christ unless they deliberately reject the truth.
This is the sense of the mystical body of Christ that I received from my Catholic education, which was a good one, in the 50’s and early 60’s. I haven’t looked it up in the Catechism so I’m open to correction but I’m pretty sure I’m right.