6 Be therefore like Him in piety, and earnest in meditation: for “the invisible things of Him are clearly seen, being understood by the things that are made;” look upon the things that are made, admire them, seek their author. If you are unlike, you will turn back; if like, you will rejoice. And when, being like Him, you shall have begun to approach Him, and to feel God, the more love increases in you, since God is love, you will perceive somewhat which you were trying to say, and yet couldest not say. Before you felt God, you thought that you could express God; you begin to feel Him, and then feelest that what thou dost feel you can not express. But when you have herein found that what thou dost feel cannot be expressed, will you be mute, will you not praise God? Will you then be silent in the praises of God, and will you not offer up thanksgivings unto Him who has willed to make Himself known unto you? Thou praised Him when you were seeking, will you be silent when you have found Him? By no means; you will not be ungrateful. Honour is due to Him, reverence is due to Him, great praise is due to Him. Consider yourself, see what you are: earth and ashes; look who it is has deserved to see, and What; consider who you are, What to see, a man to see God! I recognise not the man's deserving, but the mercy of God. Praise therefore Him who has mercy....
7. “Serve the Lord with gladness.” All servitude is full of bitterness: all who are bound to a lot of servitude both are slaves, and discontented. Fear not the servitude of that Lord: there will be no groaning there, no discontent, no indignation; no one seeks to be sold to another master, since it is a sweet service, because we are all redeemed. Great happiness, brethren, it is, to be a slave in that great house, although in bonds. Fear not, bound slave, confess unto the Lord: ascribe your bonds to your own deservings; confess in your chains, if you are desirous they be changed into ornaments....At the same time you are slave, and free; slave, because you are created such; free, because you are loved by God, by whom you were created: yea, free indeed, because you love Him by whom you were made. Serve not with discontent; for your murmurs do not tend to release you from serving, but to make you a wicked servant. You are a slave of the Lord, you are a freedman of the Lord: seek not so to be emancipated as to depart from the house of Him who frees you....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)