14 “For the Lord has chosen Sion to be an habitation for Himself”. Sion is the Church Herself; She is also that Jerusalem unto whose peace we are running, who is in pilgrimage not in the Angels, but in us, who in her better part waits for the part that will return; whence letters have come unto us, which are every day read. This city is that very Sion, whom the Lord has chosen.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)