19 “Save me now, O Lord: prosper Thou well my way, O Lord”. Because it is the day of Salvation, “save me:” because we, returning from a long pilgrimage, are separated from those who hated peace, with whom we were peaceful, and who, when we spoke to them, made war upon us without a cause; “prosper well our way” as we return, since You have become our Way.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)