Like all of God's commands, the command to rest—when we follow it—leads to two benefits: glorifying him and what would be the best for us.
By "best" I mean something that we might not see right away as the best, but as we proceed, we most likely will see that it indeed was the best for us. Our best sometimes is growing deeper in knowledge or love of and trust in Christ but can be a number of other things depending on the situation and command.
Resting at first may be hard and may not seem like the best at first. Saying no to people who are eager and excited that you join them can feel awful at first, and taking time out from some activities sometimes may lead to boredom. But within the quiet that God likes us to have is a wealth of opportunities: Creativity and reflection, including thinking about how God's omnipotence and love mean we don't need to constantly work to feel secure.
We glorify God in resting because we are obeying his command, and we are also taking part in an action that indicates in some way that we rely on God to meet our true needs. If we don't feel like we believe God will meet our needs, sometimes we start to see the truth in it when we rest. We took hours off of working for money or a certain goal and we find that the world is okay, and our needs are met. In some ways, resting reminds us we don't need to worry or be anxious.