8 When shall my longing be satisfied with good things? When, do you ask? “Your youth shall be renewed as the eagle's.” Do you then ask when your soul is to be satisfied with good things? When your youth shall be restored. And he adds, as an eagle's. Something here lies hidden; what however is said of the eagle, we will not pass over silently, since it is not foreign to our purpose to understand it. Let this only be impressed upon our hearts, that it is not said without cause by the Holy Spirit. For it has intimated unto us a sort of resurrection. And indeed the youth of the eagle is restored, but not into immortality, for a similitude has been given, as far as it could be drawn from a thing mortal to signify a thing immortal, not to demonstrate it. The eagle is said, after it becomes overpowered with bodily age, to be incapable of taking food from the immoderate length of its beak, which is always increasing. For after the upper part of its beak, which forms a crook above the lower part, has increased from old age to an immoderate length, the length of this increase will not allow of its opening its mouth, so as to form any interval between the lower beak and the crook above. For unless there be such an opening, it has no power of biting like a forceps, by which to shear off what it may put within its jaws. The upper part therefore increasing, and being too far hooked over, it cannot open its mouth, and take any food. This old age does to it, it is weighed down with the infirmity of age, and becomes too weak from want of power to eat; two causes of infirmity assaulting it, old age, and want. By a natural device, therefore, in order in some measure to restore its youth, the eagle is said to dash and strike against a rock the upper lip of its beak, by the too great increase of which the opening for eating is closed: and by thus rubbing it against the rock, it breaks off the weight of its old beak, which impeded its taking food. It comes to its food, and everything is restored: it will be after its old age like a young eagle; the vigour of all its limbs returns, the lustre of its plumage, the guidance of its wings, it flies aloft as before, a sort of resurrection takes place in it. For this is the object of the similitude, like that of the Moon, which after waning and being apparently intercepted, again is renewed, and becomes full; and signifies to us the resurrection; but when it is full it does not remain so; again it wanes, that the signification may never cease. Thus also what has here been said of the eagle: the eagle is not restored unto immortality, but we are unto eternal life; but the similitude is derived from hence, that the rock takes away from us what hinders us. Presume not therefore on your strength: the firmness of the rock rubs off your old age: for that Rock was Christ. In Christ our youth shall be restored like that of the eagle....
9. “The Lord executes mercy and judgment for all them that are oppressed with wrong”....An adulterous woman is brought forward to be stoned according to the Law, but she is brought before the Lawgiver Himself....Our Lord, at the time she was brought before Him, bending His Head, began writing on the earth. When He bent Himself down upon the earth, He then wrote on the earth: before He bent upon the earth, He wrote not on the earth, but on stone. The earth was now something fertile, ready to bring forth from the Lord's letters. On the stone He had written the Law, intimating the hardness of the Jews: He wrote on the earth, signifying the productiveness of Christians. Then they who were leading the adulteress came, like raging waves against a rock: but they were dashed to pieces by His answer. For He said to them, “He that is without sin among you, let him first cast a stone at her.” And again bending His head, He began writing on the ground. And now each man, when he asked his own conscience, came not forward. It was not a weak adulterous woman, but their own adulterate conscience, that drove them back. They wished to punish, to judge; they came to the Rock, their judges were overthrown by the Rock....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)