5 “Your throne is established from thence, O Lord”. What is, “from thence”? From that time. As if he said, What is the throne of God? Where does God sit? In His Saints. Do you wish to be the throne of God? Prepare a place in your heart where He may sit. What is the throne of God, except where God dwells? Where does God dwell, except in His temple? What is His temple? Is it surrounded with walls? Far from it. Perhaps this world is His temple, because it is very great, and a thing worthy to contain God.
It contains not Him by whom it was made. And wherein is He contained? In the quiet soul, in the righteous soul: that is it that contains Him....He who said, “Before Abraham was, I am:” not before Abraham only, but before Adam: not only before Adam, but before all the angels, before heaven and earth; since all things were made through Him: he added, lest you, attending to the day of our Lord's nativity, might think He commenced from that time, “Your throne is established, O God.”
But what God? “You are from everlasting:” for which he uses ‡ π' αἰῶνος, in the Greek version; that word being sometimes used for an age, sometimes for everlasting. Therefore, O Thou who seemest to be born “from thence,” You are from everlasting! But let not human birth be thought of, but Divine eternity. He began then from the time of His birth; He grew: you have heard the Gospel. He chose disciples, He replenished them, His disciples began to preach. Perhaps this is what he speaks of in the following verse.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)