Psalm 100:2 says " Serve the Lord with gladness." I wrote in the margin: " What if I don't ?"
Then for some reason, I wrote next to it Deut 28:47-48
It says: " Because you did not serve the Lord your God with joy and a glad heart, for the abundance of all things ; therefore you shall serve your enemies whom the Lord will send against you, in hunger, in thirst, in nakedness, and in the lack of all things; and He will put an iron yoke on your neck until He has destroyed you."
Basically... if I dont' serve with gladness... I will serve my enemies. This tells me that God takes joy very seriously. He is opposed to our complaining and murmuring.
Are you serving with gladness or a bitter spirit ?