Because of my sinfulness, I am prone by my very nature to rebel against God. One of those ways is by being inactive. While it is good to rest, and it glorifies God (who never sleeps), I can also fall into a habit of idleness.
And, when we do that, we make a god out of our rest because it becomes the thing that satisfy us rather than God. The Bible tells us that life is a “mist that appears for a little time and then vanishes.” Do we want to waste it on the drug of idleness? Rather, we need to trust God to help us in our labors and find rest in Him:
Come to me, all who labor and are heavy laden, and I will give you rest. Take my yoke upon you, and learn from me, for I am gentle and lowly in heart, and you will find rest for your souls. For my yoke is easy, and my burden is light.
— Jesus, as quoted in Matthew 11: 28-30