2 The title of this Psalm is, “A Psalm of confession.” The verses are few, but big with great subjects; may the seed bring forth within your hearts, the barn be prepared for the Lord's harvest.
3. “Jubilate,” therefore, “unto the Lord, all you lands”. This Psalm gives this exhortation to us, that we jubilate unto the Lord. Nor does it, as it were, exhort one particular corner of the earth, or one habitation or congregation of men; but since it is aware that it has sown blessings on every side, on every side it does exact jubilance. Does all the earth at this moment hear my voice? And yet the whole earth has heard this voice. All the earth is already jubilant in the Lord; and what is not as yet jubilant, will be so. For blessing, extending on every side, when the Church was commencing to spread from Jerusalem throughout all nations, everywhere overturns ungodliness, and everywhere builds up piety: the good are mingled with the wicked throughout all lands. Every land is full of the discontented murmurs of the wicked, and of the jubilance of the good. What then is it, “to jubilate”? For the title of the present Psalm especially makes us give good heed to this word, for it is entitled, “A Psalm of confession.” What means, to jubilate with confession? It is the sentiment thus expressed in another Psalm: “Blessed is the people that understands jubilance.” Surely that which being understood makes blessed is something great. May therefore the Lord our God, who makes men blessed, grant me to understand what to say, and grant you to understand what ye hear: “Blessed is the people that understands jubilance.” Let us therefore run unto this blessing, let us understand jubilance, let us not pour it forth without understanding. Of what use is it to be jubilant and obey this Psalm, when it says, “Jubilate unto the Lord, all you lands,” and not to understand what jubilance is, so that our voice only may be jubilant, our heart not so? For the understanding is the utterance of the heart.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)