6 “O God, deliver me from the hand of the sinner”. Generally, sinners, among whom is toiling he that is now to be delivered from captivity: he that now cries, “Unhappy man I, who shall deliver me from the body of this death? The grace of God through Jesus Christ our Lord.” Within is a foe, that law in the members; there are without also enemies: unto what do you cry? Unto Him, to whom has been cried, “From my secret sins cleanse me, O Lord, and from strange sins spare Your servant.”...But these sinners are of two kinds: there are some that have received Law, there are others that have not received: all the heathen have not received Law, all Jews and Christians have received Law.
Therefore the general term is sinner; either a transgressor of the Law, if he has received Law; or only unjust without Law, if he has not received the Law. Of both kinds speaks the Apostle, and says, “They that without Law have sinned, without Law shall perish, and they that in the Law have sinned, by the Law shall be judged.” But thou that amid both kinds dost groan, say to God that which you hear in the Psalm, “My God, deliver me from the hand of the sinner.” Of what sinner?
“From the hand of him that transgresses the Law, and of the unjust man.” He that transgresses the Law is indeed also unjust; for not unjust he is not, that transgresses the Law: but every one that transgresses the Law is unjust, not every unjust man does transgress the Law. For, “Where there is not a Law,” says the Apostle, “neither is there transgression.” They then that have not received Law, may be called unjust, transgressors they cannot be called. Both are judged after their deservings.
But I that from captivity will to be delivered through Your grace, cry to You, “Deliver me from the hand of the sinner.” What is, from the hand of him? From the power of him, that while he is raging, he lead me not unto consenting with him; that while he lies in wait, he persuade not to iniquity. “From the hand of the sinner and of the unjust man.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)