By Singing with a sad face is like trying to lick your elbow—it just isn’t really possible. It is true that not every person exudes their inner joy in equally expressive ways, and it is true that we worship God in the heart-breaking troubles of life too, but when we choose to sing to God, our face can’t be sad.
Throughout the ages, singing as an expression of worship to God communicates joy, celebration, praise, exaltation, thankfulness, and hope. Singing is what you do when you want to add beauty and joy to otherwise ordinary words. Singing is when you want to raise your voice and not have it mistaken for lament or anger. Singing is what you do when you want to say something in the most exuberant way possible.
The entire book of Psalms, not to mention the narratives, prophecies, and instructions in the rest of the Scriptures, portray this view of the singing of true believers. Perhaps Psalm 33:3 is a good one-verse summary of what singing is to a true worshipper.
Sing to the LORD a new song; play skillfully on the strings, with loud shouts.
Psalm 33:3
Of all the different expression of worship, singing is the most overtly joyful. Don’t sing with a sad face.