1 This Psalm has on the title the inscription, “For the end, a song of a Psalm of Resurrection.” When ye hear “for the end,” whenever the Psalms are repeated, understand it “for Christ:” the Apostle saying, “For the end of the law is Christ, for righteousness to every one believing.” In what manner therefore here Resurrection is sung, you wilt hear, and whose Resurrection it is, as far as Himself deigns to give and disclose. For the Resurrection we Christians know already has come to pass in our Head, and in the members it is to be. The Head of the Church is Christ, the members of Christ are the Church. That which has preceded in the Head, will follow in the Body. This is our hope; for this we believe, for this we endure and persevere amid so great perverseness of this world, hope comforting us, before that hope becomes reality....The Jews did hold the hope of the resurrection of the dead: and they hoped that themselves alone would rise again to a blessed life because of the work of the Law, and because of the justifications of the Scriptures, which the Jews alone had, and the Gentiles had not. Crucified was Christ, “blindness in part happened unto Israel, in order that the fullness of the Gentiles might enter in:” as the Apostle says. The resurrection of the dead begins to be promised to the Gentiles also that believe in Jesus Christ, that He has risen again. Thence this Psalm is against the presumption and pride of the Jews, for the comfort of the Gentiles that are to be called to the same hope of resurrection.
2....Thence he begins, “Be joyful in God.” Who? “Every land”. Not therefore Judæa alone. See, brethren, after what sort is set forth the universality of the Church in the whole world spread abroad: and mourn ye not only the Jews, who envied the Gentiles that grace, but still more for heretics wail ye. For if they are to be mourned, that have not been gathered together, how much more they that being gathered together have been divided? “Jubilate in God every land.” What is “jubilate”? Into the voice of rejoicings break forth if you cannot into that of words. For “jubilation” is not of words, but the sound alone of men rejoicing is uttered, as of a heart labouring and bringing forth into voice the pleasure of a thing imagined which cannot be expressed. “Be joyful in God every land:” let no one jubilate in a part: let every land be joyful, let the Catholic Church jubilate. The Catholic Church embraces the whole: whosoever holds a part and from the whole is cut off, should howl, not jubilate.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)