This aria is from Bach's St. Matthew's Passion. The text is a meditation on Peter's regret after the rooster calls, when he recognizes his betrayal of Jesus, as we find in Matthew 26:75.
Bach understands that in crying over his sin, Peter must have also been asking for Christ's mercy.
Erbarme dich, mein Gott,
Have mercy, my God
Um meiner Zähren Willen!
for the sake of my tears!
Schaue hier, Herz und Auge
Look here, heart and eyes
Weint vor dir bitterlich.
weep bitterly before you.
Erbarme dich, erbarme dich!
Have mercy, have mercy!