8 “The Lord is my strength and my praise, and has become my salvation”. Who then fall, when they are pushed, save they who choose to be their own strength and their own praise? For no man falls in the contest, except he whose strength and praise fails. He therefore whose strength and praise is the Lord, falls no more than the Lord falls. And for this reason He has become their salvation; not that He has become anything which He was not before, but because they, when they believed on Him, became what they were not before, and then He began to be salvation unto them when turned towards Him, which He was not to them when turned away from Himself.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)