4 For many weep with the weeping of Babylon, because they rejoice also with the joy of Babylon. When men rejoice at gains and weep at losses, both are of Babylon. You ought to weep, but in the remembrance of Sion. If you weep in the remembrance of Sion, you ought to weep even when it is well with you in Babylon....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)