9 But what that is which he says, “they have been turned back in the day of war,” the following words do teach, wherein he has most clearly explained this: “they have not kept,” he says, “the testament of God, and in His law they would not walk”. Behold what is, “they have been turned back in the day of war:” they have not kept the testament of God. When they were bending and shooting bows, they did also utter the words of most forward promise, saying, “Whatsoever things the Lord our God has spoken we will do, and we will hear.” “They have been turned back in the day of war:” because the promise of obedience not hearing but temptation does prove. But he whose spirit has been trusted with God, keeps hold on God, who is faithful, and “does not suffer him to be tempted above that which he is able; but will make with the temptation a way of escape also,” that he may be able to endure, and may not be turned back in the day of war....Therefore these men have been thus branded: “a generation,” he says, “which has not directed their heart.” It has not been said, works, but heart. For when the heart is directed, the works are right; but when the heart is not directed, the works are not right, even though they seem to be right. And how the crooked generation has not directed the heart, has sufficiently been shown, when he says, “and the spirit thereof has not been trusted with God.” For God is right: and therefore by cleaving to the right, as to an immutable rule, the heart of a man can be made right, which in itself was crooked....
10. “And they forgat His benefits, and the wonderful works of Him which He showed to them; before their fathers the wonderful things which He did”. What this is, is not a question to be negligently passed over. Concerning those very fathers he was speaking a little before, that they had been a generation crooked and embittering....What fathers, inasmuch as these are the very fathers, whom he would not have posterity to be like? If we shall take them to be those out of whom the others had derived their being, for example, Abraham, Isaac, Jacob, by this time they had long since fallen asleep, when God showed wonderful things in Egypt. For there follows, “in the land of Egypt, in the plain of Thanis”: where it is said that God showed to them wonderful things before their fathers. Were they perchance present in spirit? For of the same the Lord says in the Gospel, “for all do live to Him.” Or do we more suitably understand thereby the fathers Moses and Aaron, and the other elders who are related in the same Scripture also to have received the Spirit, of which also Moses received, in order that they might aid him in ruling and bearing the same people? For why should they not have been called fathers? It is not in the same manner as God is the One Father, who does regenerate with His Spirit those whom He does make sons for an everlasting inheritance; but it is for the sake of honour, because of their age and kindly carefulness: just as Paul the elder says, “Not to confound you I am writing these things, but as my dearly beloved sons I am admonishing you:” though he knew of a truth that it had been said by the Lord, “Call ye no man your father on earth, for One is your Father, even God.” And this was not said in order that this term of human honour should be erased from our usual way of speaking: but lest the grace of God whereby we are regenerated unto eternal life, should be ascribed either to the power or even sanctity of any man. Therefore when he said, “I have begotten you;” he first said, “in Christ,” and “through the Gospel;” lest that might be thought to be of him, which is of God....Accordingly, the land of Egypt must be understood for a figure of this world. “The plain of Thanis” is the smooth surface of lowly commandment. For lowly commandment is the interpretation of Thanis. In this world therefore let us receive the commandment of humility, in order that in another world we may merit to receive the exaltation which He has promised, who for our sake here became lowly.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)