17 “In evening, in morning, at noon-day I will recount and will tell forth, and He shall hearken to my voice”. Do thou proclaim glad tidings, keep not secret that which you have received, “in evening” of things gone by, “in morning” of things to be, at “noonday” of things ever to be. Therefore, to that which he says “in evening” belongs that which he recounts: to that which he says, “in morning,” belongs that which he tells forth: to that which he says “at noon-day,” belongs that wherein his voice is hearkened to.
For the end is at noon-day; that is to say, whence there is no going down unto setting. For at noon-day there is light full high, the splendour of wisdom, the fervour of love. “In evening and in morning and at noon-day.” “In evening,” the Lord on the Cross; “in morning,” in Resurrection; “at noon-day,” in Ascension. I will recount in evening the patience of Him dying, I will tell forth in morning the life of Him rising, I will pray that He hearken at noon-day sitting at the right hand of the Father.
He shall hearken to my voice, That intercedes for us. How great is the security of this man. How great the consolation, how great the refuge “from weakness of mind and tempest,” against evil men, against ungodly men both without and within, and in the case of those that are without though they had been within.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)