1 Very pleasant ought it be to us, and we should rejoice because it is pleasant, to which this Psalm exhorts us. For it says, “Praise the name of the Lord”. And it immediately appends the reason, why it is just to praise the name of the Lord. “Praise the Lord, you servants.” What more just? What more worthy? What more thankful?...For if He teaches His own servants who have deserved well of Him, the preachers of His Word, the rulers of His Church, the worshippers of His name, the obeyers of His command, that in their own conscience they should possess the sweetness of their life, lest they be corrupted by the praise or disheartened by the reproach of men; how much the more is He above all, the unchangeable One, who teaches these things, neither the greater if you praise, or the less if you reproach. For you will do nothing out of place, by praising your Lord, as servants. And if you were to be for ever only servants, you ought to praise the Lord; how much more ought ye servants to praise the Lord, that you may hereafter gain the privilege of sons?
2....Therefore, “You who stand in the house of the Lord, in the courts of the house of our God, praise the Lord”. Be thankful; you were without, and you stand within. Since then ye stand, is it a small thing for you to think where He should be praised, who raised you when you were cast down, and caused you to stand in His house, to know Him, and to praise Him? Is it a small boon, that we stand in the house of the Lord?...If one thinks of this, and is not unthankful, he will utterly despise himself in comparison with the love of his Lord, who has done so great things for him. And since he has nothing wherewith to repay God for so great benefits, what remains for him but to give Him thanks, not to repay Him? It belongs to the very act of thanksgiving, to “receive the cup of the Lord, and to call upon His name.” For what can the servant repay the Lord for all that He has given him?
Source: The Enarrations, or Expositions, on the Psalms (New Advent)