1....It is entitled, “The Song of praise of David himself, on the day before the Sabbath, when the earth was founded.” Remembering then what God did through all those days, when He made and ordained all things, from the first up to the sixth day (for the seventh He sanctified, because He rested on that day after all the works, which He made very good), we find that He created on the sixth day (which day is here mentioned, in that he says, “before the Sabbath”) all animals on the earth; lastly, He on that very day created man in His own likeness and image.
For these days were not without reason ordained in such order, but for that ages also were to run in a like course, before we rest in God. But then we rest if we do good works. As a type of this, it is written of God, “God rested on the seventh day,” when He had made all His works very good. For He was not wearied, so as to need rest, nor has He now left off to work, for our Lord Christ says openly, “My Father works hitherto.” For He says this unto the Jews, who thought carnally of God, and understood not that God works in quiet, and always works, and is always in quiet.
We also, then, whom God willed then to figure in Himself, shall have rest after all good works....And because these good works are doomed to pass away, that sixth day also, when those very good works are perfected, has an evening; but in the Sabbath we find no evening, because our rest shall have no end: for evening is put for end. As therefore God made man in His own image on the sixth day: thus we find that our Lord Jesus Christ came into the sixth age, that man might be formed anew after the image of God.
For the first period, as the first day, was from Adam until Noah: the second, as the second day, from Noah unto Abraham: the third, as the third day, from Abraham unto David: the fourth, as the fourth day, from David unto the removal to Babylon: the fifth period, as the fifth day, from the removal to Babylon unto the preaching of John. The sixth day begins from the preaching of John, and lasts unto the end: and after the end of the sixth day, we reach our rest. The sixth day, therefore, is even now passing. And it is now the sixth day, see what the title has; “On the day before the Sabbath, when the earth was founded.”
Let us now listen to the Psalm itself: let us enquire of it, how the earth was made, whether perhaps the earth was then made: and we do not read so in Genesis. When, therefore, was the earth founded? When, unless when that which has been but now read in the Apostle takes place: “If,” he says, “you are steadfast, immovable.” When all who believe throughout all the earth are steadfast in faith, the earth is founded: then man is made in the image of God. That sixth day in Genesis signifies this....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)