5 “For the Lord has chosen Jacob to Himself, Israel for His own possession”....Let not Jacob therefore extol himself, let him not boast himself, or ascribe it to his own merits. He was known before, predestinated before, elected before, not elected for his own merits, but found out, and gifted with life by the grace of God. So with all the Gentiles; for how did the wild-olive deserve, that it should be grafted in, from the bitterness of its berries, the barrenness of its wildness? It was the wood of the wilderness, not of the Lord's field, and yet He of His mercy grafted the wild-olive into the (true) olive. But up to this time the wild-olive was not grafted in.
6....“Because,” says he, “I know that the Lord is great, and our God is above all gods”. If we should say to him, we ask you, explain to us His greatness; would he not perchance answer us, He whom I see is not so very great, if He be able to be expounded by me. Let him then return to His works, and tell us. Let him hold in his conscience the greatness of God, which he has seen, which he has committed to our faith, whither he could not lead our eyes, and enumerate some of the things which the Lord has done here; that unto us, who cannot see His greatness as he can, He may become sweet through the works of His which we can comprehend....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)