26 But of them he says what? “They shall not halve their days.” What is, “They shall not halve their days”? They shall not make progress as much as they think: within the time which they expect, they shall perish. For he is that partridge, whereof has been said, “In the half of his days they shall leave him, and in his last days he shall be an unwise one.” They make progress, but for a time. For what says the Apostle? “But evil men and seducers shall make progress for the worse, themselves erring, and other men into error driving.” But “a blind man leading a blind man, together into a ditch they fall.” Deservedly they fall “into the pit of corruption.”
What therefore says he? They shall make progress for the worse: not however for long. For a little before he has said, “But further they shall not make progress:” that is, “shall not halve their days.” Let the Apostle proceed and tell wherefore: “For the madness of them shall be manifest to all men, as also was that of the others.” “But I in You will hope, O Lord.” But deservedly they shall not halve their days, because in man they have hoped. But I from days temporal have reached unto day eternal. Wherefore? Because in You I have hoped, O Lord.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)