2 “O Lord my God, in You have I hoped: save me from all them that persecute me, and deliver me”. As one to whom, already perfected, all the war and enmity of vice being overcome, there remains no enemy but the envious devil, he says, “Save me from all them that persecute me, and deliver me: lest at any time he tear my soul as a lion.” The Apostle says, “Your adversary the devil, as a roaring lion, walks about, seeking whom he may devour.” Therefore when the Psalmist said in the plural number, “Save me from all them that persecute me:” he afterwards introduced the singular, saying, “lest at any time he tear my soul as a lion.” For he does not say, lest at any time they tear: he knew what enemy and violent adversary of the perfect soul remained. “Whilst there be none to redeem, nor to save:” that is, lest he tear me, while Thou redeemest not, nor savest. For, if God redeem not, nor save, he tears.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)