1 Of this Psalm the title is, “A song of a Psalm of Asaph.” We have already often said what is the interpretation of Asaph, that is, congregation. That man, therefore, who was called Asaph, is named in representation of the congregation of God's people in the titles of many Psalms. But in Greek, congregation is called synagogue, which has come to be held for a kind of proper name for the Jewish people, that it should be called The Synagogue; even as the Christian people is more usually called The Church, in that it too is congregated.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)