Marquis de Lafayette is best know for is aid to the Americans during the revolution were he fought along side them to help win the war
I think it is let no one hear.
I believe you are referring to the book of John in the bible
the book of john cautions against syncretism of christian religion and the holding of doctrines that are heretical.
syncretism is the mixing of various views into a culture or religion, that was spreading quickly in the early church.