13 “The Lord strengthens all that are falling”. But who are “all that are falling”? All indeed fall in a general sense, but he means those who fall in a particular way. For many fall from Him, many also fall from their own imaginations. If they had evil imaginations, they fall from them, and “God strengthened all that are falling.” They who lose anything in this world, yet are holy, are as it were dishonoured in this world, from rich become poor, from honoured of low estate, yet are they God's saints; they are, as it were, falling. But “God strengthens.” For “the just falls seven times, and rises again; but the wicked shall be weakened in evils.” When evils befall the wicked, they are weakened thereby; when evils befall the righteous, “the Lord strengthens all that are falling.”...“And lifts up all those that have been cast down:” all, that is, who belong to him; for “God resists the proud.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)