Nevertheless the passions, whether violent or not, should never be so expressed as to reach the point of causing disgust and music, even in situations of the greatest horror, should never be painful to the ear but should flatter and charm it, and thereby always remain music.

Mozart is articulating an aesthetic principle about musical expression: even when portraying extreme emotions or terrifying dramatic situations, music should not become physically unpleasant or repellent. The composer’s task is to convey passion and horror through artful means—harmony, melody, orchestration, and pacing—so that the listener remains engaged rather than alienated. The remark implies a boundary between expressive intensity and mere noise or ugliness: music may depict suffering, rage, or dread, but it should still “flatter and charm” the ear in its sound. It also reflects an 18th‑century ideal of decorum, where art transforms raw feeling into a refined, communicable form.