The paper proposes a philosophical interpretation of Monteverdi's madrigal. To the question: "What makes the unity and the principle of the work?", it answers: an aesthetic theory of expression and a theological conception of incarnation. This dual theory explains the "agitated style" that had been created to express the most violent passions of human soul. It is the use of evocative musical figures that allows the meeting of vision and audition. The vibrations and the trembling of the voice ensure their exchangeability.