This WAS, at one time (when ALL the Christian world was Roman Catholic) the prime consideration for participating in the Eucharist. It is still the prime consideration in CATHOLIC Anglican and Episcopal churches...HOWEVER, the Roman church requires that all desiring the Eucharist must first make a confession (which is exclusive to RCs and in which case we all know that St. Bubba would try to convince the priest what "is" is) while Episcopalians and Anglican catholics recite a general confession.
There has never been a time when "ALL the Christian was Roman Catholic", as you stated.