1....Let them “lift up their eyes to the hills whence comes their help”. What means, The hills have been lightened? The San of righteousness has already risen, the Gospel has been already preached by the Apostles, the Scriptures have been preached, all the mysteries have been laid open, the veil has been rent, the secret place of the temple has been revealed: let them now at length lift their eyes up to the hills, whence their help comes...“Of His fullness have all we received,” he says. Your help therefore is from Him, of whose fullness the hills received, not from the hills; towards which, nevertheless, save thou lift your eyes through the Scriptures, you will not approach, so as to be lighted by Him.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)