The soul is imprisoned in the body, and the Lord... built two windows in the wall of the prison... Unfortunately, the windows have curtains—eyelids; and a man whose soul is impure, feeling himself scrutinized, lets down the curtains and conceals the soul.

Mesiras Nefesh, quoted in M. Samuel. Prince of the Ghetto. Alfred A. Knopf, 1948, p. 22.