28 “His seed will I make to endure world without end”. Not only for this world, but unto the world without end: whither His seed, which is His heritage, the seed of Abraham, which is Christ, will pass. But if you are Christ's, you are also Abraham's seed: and if you are destined His heirs for ever, “He will establish His seed unto world without end: and His throne as the days of Heaven.” The thrones of earthly kings are as the days of the earth: different are the days of Heaven from those of earth. The days of Heaven are those years of which it is said, “You are the same, and Your years shall not fail.” The days of the earth are soon overtaken by their successors: those which precede are shut out from us: nor do those which succeed remain: but they come that they may go, and are almost gone before they have come. Such are the days of earth. But the days of Heaven, which are also the “One day” of Heaven, and the never failing years, have neither beginning nor end: nor is any day there narrowed between yesterday and tomorrow: no one there expects the future, nor loses the past: but the days of Heaven are always present, where His throne shall be for ever and ever....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)