Augustine of Hippo

"O serve the Lord with gladness" (ver. 2): he addresseth you, whoever ye are who endure all things in love, and rejoice in hope. "Serve the Lord," not in the bitterness of murmuring, but in the "gladness of love." "Come before His presence with rejoicing." It is easy to rejoice outwardly: rejoice before the presence of God. Let not the tongue be too joyful: let the conscience be joyful. "Come before His presence with a song."