A Joyous Heart - Pleasing to God
You should be joyful in Christ, your gracious Lord and Redeemer. Let Him take care of you. For He assuredly does take care of you though as yet you do not have what you would like to have. He still lives. Expect the best from Him; this (as Scripture says) pleases Him as the best of sacrifices. For there is no sacrifice lovelier and more pleasing than a cheerful heart, joyful in the Lord. Therefore when you are sad, and this spirit threatens to gain the upper hand, you should say: Come on! I must play our Lord Christ a song on the organ (be it the Te Deum laudamus or the Benedictus, etc.), for Scripture teaches me that He is pleased to hear a cheerful song and the music of stringed instruments.
(What Luther Says - p. 690 - para 2139)