7 And he returns to this, “From the morning watch let Israel hope in the Lord.” Not only “let Israel hope,” but “from the morning watch let Israel hope.” Do I then blame the hope of the world, when it is placed in the Lord? No; but there is another hope belonging to Israel. Let not Israel hope for riches as his highest good, not for health of body, not for abundance of earthly things: he will indeed have to suffer tribulation here, if it should be his lot to suffer any troubles for the sake of the truth....
8. “For with the Lord there is mercy, and with Him is plenteous redemption”. Admirable! This could not have been better said in its own place, on account of the words, “From the morning watch.” Wherefore? Because the Lord rose again from the morning watch; and the body ought to hope for that which went before in the Head. But, lest this thought should be suggested: The Head might rise again, because It was not weighed down with sins, there was no sin in Him; what shall we do? Shall we hope for such a resurrection, as went before in the Lord, while we are weighed down by our sins? But see what follows: “And He shall redeem Israel from all his sins”. Though therefore he was weighed down with his sins, the mercy of God is present to him. For this reason, He went before without sin, that He may blot out the sins of those that follow Him. Trust not in yourselves, but trust from the morning watch....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)