Act IV was given over almost entirely to the threat posed to the romantic love theme and was dominated by the figure of Shylock. In the play's last act, consisting of only this scene, we return to Belmont — the world of comedy and romance. The opening dialogue between Lorenzo and Jessica reestablishes the atmosphere of harmony.
Lorenzo's opening words call upon us to imagine that the lovers are surrounded by night and moonlight, "when the sweet wind did gently kiss the trees." Their dialogue is used to create the general atmosphere of love and night and moonlight, thus establishing the tone of the scene. Lorenzo introduces the theme of love and moonlight with two speeches of great beauty. In the early lines of the act (55-65), he introduces the idea that music is the "music of the spheres." This was a popular Elizabethan notion, according to which the revolution of each planet around the earth produced a sound, and the combination of all the individual sounds of the planets made a "divine harmony."
Lorenzo's next speech also concerns music. Having summoned Portia's own personal musicians, he signals them to play, and he elaborates on the nature of music to Jessica. Significantly, music is very often an important element in Shakespeare's plays, both as a theatrical device and also as a general criterion of character. Those characters who dislike music are invariably incomplete or distorted human beings. Here, Lorenzo underlines the idea that "the man that hath no music in himself . . . Let no such man be trusted."
