LEV111 The fourth principle [of repentance] is grief over one's actions, as the pasuk says (Yoel 2:12), "Even now, so declares Hashem: Return to Me with all your hearts, and with fasting, weeping, and lamenting." Our sages, z"l, said (Yerushalmi Berachos 1:5, Bamidbar Rabbah 17:7), "The heart and the eyes are the two agents of sin." Similarly, it states (Bemidbar 15:39), "You must not explore after your heart and your eyes." Atoning for the transgression of these agents requires that their repentance be commensurate with their waywardness. The transgression of the hearts of the sinners is atoned for through their bitterness and sighing, by breaking their hearts [in sorrow over the sin committed] -- as it is written (Yeshayahu 57:16), "Until the spirit be Me surrenders," and as the pasuk says (Tehillim 51:19), "A heart broken and crushed, Hashem, You will not distain" [This is a reference to the first agent of sin -- the heart; consequently, one must have a broken heart to atone for the sins of the heart.) This can be compared to impure vessels which, when broken, are purified from their defilement, as the pasuk says [this verse], "A [clay] oven or a stove shall be shattered." The transgression of the eyes are atoned for by tears, as the pasuk says success (Tehillim 119:136), "Streams of water run down from my eyes because they did not keep Your Torah." It does not say "because I did not keep Your Torah," but rather "[because] they did not keep." Since they were the cause of sin, therefore, I have shed streams of water (This is a reference to the second agent of sin; consequently, one must shed tears to atone for the transgression of his eyes).