20 “Blessed be the Lord God of Israel, who has done wonderful things alone”. Contemplating all things above spoken of, a hymn bursts forth; and the Lord God of Israel is blessed. For that is being fulfilled which has been spoken to that barren woman, “and He that has delivered You, the God of Israel, shall Himself be called of the whole earth.” “He does” Himself “marvellous things alone:” for whosoever do them, He does Himself work in them, “who does wonderful things alone.”
“And blessed be the name of His glory for everlasting, and for age of age”. For what else should the Latin interpreters have said, who could not have said for everlasting, and for everlasting of everlasting? For it sounds as if one thing were meant in the expression “for everlasting,” and another thing in the expression “for age:” but the Greek has εἰς τὸν αἰωνα, καὶ εἰς τὸν αἰῶνα τοῦ αἰῶνος, which perchance more meetly might have been rendered by, “for age, and for age of age:” so that by “for age,” might have been understood as long as this age endures; but “for age of age,” that which after the end of this is promised to be.
“And there shall be fulfilled with the glory of Him every land: so be it, so be it.” You have commanded, O Lord, so it is coming to pass: so it is coming to pass, until that which began with the river, may attain fully even unto the ends of the round world.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)