16 In all these things shall we not rejoice? Or shall we contain our joy? Or shall words suffice for our gladness? Or shall the tongue be able to express our rejoicing? If therefore no words suffice, “Blessed is the people, O Lord, that knows glad shouting”. O blessed people! Do you conceive aright, do you understand, glad shouting? For except thou understand glad shouting, you can not be blessed. What do I mean by understanding glad shouting? Whether you know the source of that rejoicing which is beyond words to express.
For this joy is not of yourself, since “he that glories, let him glory in the Lord.” Rejoice not then in your own pride, but in God's grace. See that that grace is such, that the tongue fails to express its greatness, and then you understand glad shouting....O Lord, “they shall walk in the light of Your countenance.” “They shall rejoice in Your name all the day”. That Thabor and Hermon shall rejoice in Your name: all day shall they rejoice, if they will, in Your name; but if they will rejoice in their own name, they shall not rejoice all day: for they shall not continue in their joy, when they shall delight in themselves, and fall through pride.
That they may rejoice all day, therefore, “they shall rejoice in Your name, and in Your righteousness shall they be exalted.” Not in their own, but in Yours: lest they have a zeal of God, but not according to knowledge. For some are noted by the Apostle, that they have a zeal of God, but not according to knowledge, “being ignorant of God's righteousness, and going about to establish their own,” and not rejoicing in Your light, and thus “not submitting themselves unto the righteousness of God.” And why?
Because “they have a zeal of God, but not according to knowledge.” But the people who knows glad shouting (for the former err from want of knowledge, but blessed is the people not that knows not, but that knows glad shouting), whence ought it to shout, whence to rejoice, but in Your name, walking in the light of Your countenance? And it shall deserve to be exalted, but in Your righteousness: let every man take away altogether his own righteousness, and be trembled: the righteousness of God shall come, and he shall be exalted, “and in Your righteousness shall they be exalted.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)