"My dear, if my dress was bronze, you would hear the tocsin ring."
Original: "Ma chère, si ma robe était de bronze, vous entendrez sonner le tocsin."
Can you give a source for the quote identifying it with Cardinal Richelieu?
The phrase is a joke meaning approximately "You are giving me a large erection". A cardinal would have been wearing a long outer robe like a soutane. The reference to a tocsin and to bronze is to a church bell, which is rung when the large clapper, hanging down inside the bell (the dress of bronze) strikes the inside rim of the bell. So he is saying "if my clothing was a bell you would hear my clapper ringing the bell"
This isn't really a historical question.