18 But what is, “Depart from evil”?. It is little that thou injure none, murder none, steal not, commit not adultery, do no wrong, speak no false witness; “Depart from evil.” When you have departed, you say, Now I am safe, I have done all, I shall have life, I shall see good days. Not only says he, “Depart from evil,” but also, “and do good.” It is nothing that thou spoil not: clothe the naked. If you have not spoiled, you have declined from evil; but you will not do good, except thou receive the stranger into your house. So then depart from evil, as to do good. “Seek peace, and ensue it.” He has not said, You shall have peace here; seek it, and ensue it. Whither shall I ensue it? Whither it has gone before. For the Lord is our peace, has risen again, and has ascended into Heaven. “Seek peace, and ensue it;” because when thou also hast risen, this mortal shall be changed, and you shall embrace peace there where no man shall trouble you. For there is perfect peace, where you will not hunger....
19. “The Eyes of the Lord are upon the righteous:” fear not then; labour; the eyes of the Lord are upon you. “And His Ears are open unto their prayers”. What would you more? If an householder in a great house should not hearken to a servant murmuring, he would complain, and say, What hardship do we here suffer, and none hears us. Can you say this of God, What hardships I suffer, and none hears me? If He heard me, haply, do you say, He would take away my tribulation: I cry unto Him, and yet have tribulation. Only do thou hold fast His ways, and when you are in tribulation, He hears you. But He is a Physician, and still have you something of putrefaction; you cry out, but still He cuts, and takes not away His Hand, until He has cut as much as pleases Him. For that Physician is cruel who hears a man, and spares his wound and putrefaction. How do mothers rub their children in the baths for their health. Do not the little ones cry out in their hands? Are they then cruel because they spare not, nor hearken unto their tears? Are they not full of affection? And yet the children cry out, and are not spared. So our God also is full of charity, but therefore seems He not to hear, that He may spare and heal us for everlasting.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)