6 Let us see then what he seeks, with what right he has said, “quickly hear me.” For what do you seek, that you should quickly be heard? “You shall multiply me.” In many ways may multiplication be understood....For men are multiplied in their soul with cares: a man seems to be multiplied in soul, in whom vices even are multiplied. That is the multiplication of want, not of fullness. What then do you desire, thou who hast said, “quickly hear me,” and hast withdrawn yourself entirely from the body, from every earthly thing, from every earthly desire, so as to say to God, “You shall multiply me in my soul”? Explain yet further what you desire. You shall multiply me, says he, in my soul “with virtue.”...
7. “Let all the kings of the earth confess to You, O Lord”. So shall it be, and so it is, and that daily; and it is shown that it was not said in vain, save that it was future. But neither let them, when they confess to You, when they praise You, desire earthly things of You. For what shall the kings of the earth desire? Have they not already sovereignty? Whatever more a man desire on earth, sovereignty is the highest point of his desire. What more can he desire? It must needs be some loftier eminence. But perhaps the loftier it is, the more dangerous. And therefore the more exalted kings are in earthly eminence, the more ought they to humble themselves before God. What do they do? “Because they have heard all the words of Your mouth.” In a certain nation were hidden the Law and the Prophets, “all the words of Your mouth:” in the Jewish nation alone were “all the words of Your mouth,” the nation which the Apostle praises, saying, “What advantage has the Jew? Much every way; chiefly because that unto them were committed the oracles of God.” These were the words of God....What meant Gideon's fleece? It is like the nation of the Jews in the midst of the world, which had the grace of sacraments, not indeed openly manifested, but hidden in a cloud, or in a veil, like the dew in the fleece. The time came when the dew was to be manifested in the floor; it was manifested, no longer hidden. Christ alone is the sweetness of dew: Him alone you recognise not in Scripture, for whom Scripture was written. But yet, “they have heard all the words of your mouth.”
8. “And let them sing in the paths of the Lord, that great is the glory of the Lord”. Let all the kings of the earth sing in the paths of the Lord. In what paths? Those that are spoken of above, “in Your mercy and Your truth.” Let not then the kings of the earth be proud, let them be humble. Then let them sing in the ways of the Lord, if they be humble: let them love, and they shall sing. We know travellers that sing; they sing, and hasten to reach the end of their journey. There are evil songs, such as belong to the old man; to the new man belongs a new song. Let then the kings of the earth too walk in Your paths, let them walk and sing in Your paths. Sing what? That “great is the glory of the Lord,” not of kings.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)