Learn to Work in the Spirit
A big part of being able to rest in the Lord is doing your part in the spirit, so that you have full confidence to let the Lord do what only He can do, and you’re not trying to take too much on yourself.
Also, the more you learn to work in the spirit—by using your spiritual weapons, committing things to the Lord, and resting on His strength, going with His choice of priorities—the more relaxed and trusting you will be, because you’ll see that it really works, that He does what you cannot do, and that if you commit it all to Him and let Him do it, it works even better than when you try to “help” in the flesh.
Of course‚ the Lord requires us to do our part.
But learning what is your part and what is the Lord’s part, through asking Him instead of just assuming, is key.