Jacques-Bénigne Bossuet on Heresy

“The essence of the heretic, that is to say of someone who has a particular opinion, is that he clings to his own ideas; and the essence of the Catholic, that is to say of the universal, is to prefer to his sentiments the common sentiment of the entire Church.”

“And so we get an idea of the real fundamental meaning of the words Catholic and heretic. A heretic is one who has his own opinion. What does having an opinion mean? It means following one's own ideas, one's own particular notions. Whereas the Catholic, on the other hand, is what the name signifies, that is to say one who, not relying on his own private judgement, puts his trust in the Church, and defers to her teaching.”