Worry and anxiety are not merely bad habits or idiosyncrasies. They are sinful fruits that blossom from the root of unbelief. Jesus doesn’t treat obsession with the future as a personal quirk, but as evidence of little faith (Matthew 6:30). Worry and anxiety reflect our hearts’ distrust in the goodness and sovereignty of God. Worry is a spiritual issue and must be fought with faith. We must fight to believe that God has mercy for today’s troubles and, no matter what may come tomorrow, that God will have new mercies for tomorrow’s troubles (Lamentations 3:22-23). God’s way is not to show us what tomorrow looks like or even to tell us what decisions we should make tomorrow. That’s not His way because that’s not the way of faith. God’s way is to tell us that He knows tomorrow, He cares for us, and therefore, we should not worry.
– Kevin DeYoung, Just Do Something, pp. 56-57.