32 But in all these blessings of His, God does commend in Abraham the merit of faith. For the Psalmist goes on to say, “For why? He remembered His holy promise, which He made to Abraham His servant”. “And He brought forth His people with joy, and His chosen with gladness”. What he said, “His people,” he has repeated in, “His chosen.” So also what he said, “with joy,” he has repeated in, “with gladness.” “And gave them the lands of the heathen: and they took the labours of the people in possession”. “The lands of the heathen,” and “the labours of the people,” are the same; and the words, “He gave,” are repeated in these, “they took in possession.”
33....“That they may keep His statutes, and seek out His law”. Lastly, since by the seed of Abraham he wished those to be understood here, who were truly the seed of Abraham, such as were not wanting even in that people; as the Apostle Paul clearly shows, when he says, “But not in all of them was God well pleased;” for if He was not pleased with all, surely there were some in whom He was well pleased: since then this Psalm praises such men as this, he has said nothing here of the iniquities and provocations and bitterness of those with whom God was not well pleased. But since not only the justice but also the mercy of Almighty God, the merciful, was shown even unto the wicked; concerning these attributes the rest of the Psalm pursues the praises of God. And yet both sorts were in one people: nor did the latter pollute the good with the contagion of their iniquities. For “the Lord knows who are His;” and if he cannot separate in this world from wicked men, yet, “let every one that names the name of Christ depart from iniquity.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)