12 “The nations shall be troubled”. At first they shall be troubled: but those mountains prepared in the strength of Christ, are they troubled? Troubled is the sea, against the mountains it dashes: the sea breaks, unshaken the mountains have remained. “The nations shall be troubled, and all men shall fear.” Behold now all men fear: they that before have been troubled do now all fear. The Christians feared not, and now the Christians are feared. All that did persecute do now fear.
For He has overcome that is girded about with power, to Him has come every flesh in such sort, that the rest by their very minority do now fear. And all men shall fear, that inhabit the ends of the earth, because of Your signs. For miracles the Apostles wrought, and thence all the ends of the earth have feared and have believed. “Outgoings in morning and in evening You shall delight:” that is, You make delightful. Already in this life what is there being promised to us? There are outgoings in morning, there are outgoings in the evening.
By the morning he signifies the prosperity of the world, by the evening he signifies the trouble of the world....At first when he was promising gain, it was morning to you: but now evening draws on, sad you have become. But He that has given you an outgoing in the morning, will give one also in the evening. In the same manner as you have contemned the morning of the world by the light of the Lord, so contemn the evening also by the sufferings of the Lord, in saying to your soul, What more will this man do to me, than my Lord has suffered for me?
May I hold fast justice, not consent to iniquity. Let him vent his rage on the flesh, the trap will be broken, and I will fly to my Lord, that says to me, “Do not fear them that kill the body, but the soul are not able to kill.” And for the body itself He has given security, saying, “A hair of your head shall not perish.” Nobly here he has set down, “You will delight outgoings in morning and in evening.” For if you take not delight in the very outgoing, you will not labour to go out thence. You run your head into the promised gain, if you are not delighted with the promise of the Saviour. And again you yield to one tempting and terrifying, if you find no delight in Him that suffered before you, in order that He might make an outgoing for you.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)