6 What does the Psalm add? “In His hand are all the corners of the earth”: we recognise the corner stone: the corner stone is Christ. There cannot be a corner, unless it has united in itself two walls: they come from different sides to one corner, but they are not opposed to each other in the corner. The circumcision comes from one side: the uncircumcision from the other; in Christ both peoples have met together: because He has become the stone, of which it is written, “The stone which the builders rejected, has become the head of the corner.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)