It would be interesting to see a TL in which Protestantism is stillborn. The line of separation between church and state prior to the Reformation, when it existed at all, was fuzzy. I could see a more politically powerful "church" in which the line of separation is ill-defined and Europe is "unified" (whatever unified might mean to the writer of the TL) under the Catholic church.
Combine the above with an enlightened RCC controlling spiritual and intellectual education. If the RCC had maintained the education of future clergy, royalty, merchants, soldiers and statesmen; then the message would be unified.
The other element would be for the RCC to allow parish / village clergy to marry and have families like many of the Asia Minor Churches allow.