4 Lastly, there follows, “And let just men be joyous, and exult in the sight of God, let them delight in gladness”. For then shall they hear, “Come, you blessed of My Father, receive ye the kingdom.” “Let them be joyous,” therefore, that have toiled, “and exult in the sight of God.” For there will not be in this exultation, as though it were before men, any empty boasting; but (it will be) in the sight of Him who unerringly looks into that which He has granted. “Let them delight in gladness:” no longer exulting with trembling, as in this world, so long as “human life is a trial upon earth.” Secondly, he turns himself to those very persons to whom he has given so great hope, and to them while here living he speaks and exhorts: “Sing ye to God, psalm ye to His name”.
Already on this subject in the exposition of the Title we have before spoken that which seemed meet. He sings to God, that lives to God: He psalms to His name, that works unto His Glory. In singing thus, in psalming thus, that is, by so living, by so working, “a way make ye to Him,” he says, “that has ascended above the setting.” A way make ye to Christ: so that through the beautiful feet of men telling good tidings, the hearts of men believing many have a way opened to Him. For the Same is He that has ascended above the “setting:” either because the new life of one turned to Him receives Him not, except the old life shall have set by his renouncing this world, or because He ascended above the setting, when by rising again He conquered the downfall of the body.
“For The Lord is His name.” Which if they had known, the Lord of glory they never would have crucified.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)