Saename,
My understanding is that Rome was a very cosmopolitan society and that the Emperor was concerned at the disharmony within Christianity, including within Pauline Christianity. I suspect that although this sect was "selected", it was not the dominant form.
My position is that Constantine and Theodosius intervened to bring the internal Pauline disharmony to an end, and in the process imposed the positions held by one part of that sect (that's where Trinitarianism rears its head).
Regarding "shall". My first editor, and we are talking about 1971, refused anyone the use of the word "will". He said that something happened or it did not. Secondly, I read that the English and the Scots use "will" and "shall" with opposite meaning. (I think the reference was a book by Fowler. Was it an English Government style book? I wonder whether the Chicago Style Manual discusses "will" versus "shall". There are, of course, differences in the English language between the correct version - Australian - and all other versions.)
Out of all that, I use will to mean "I want to" and I use shall to mean "I am going to". Apologise for the quirks in my old mind.
I get annoyed when I hear someone say that "such-and-such prevented this from happening". In my mind, the word "from" is unnecessary.
I am sure that I will get comments and criticisms on my upcoming Study.
Doug