This is the key to finding rest in your suffering. There is only one way in which rest is to be found: to let God rule in everything. Whatever else you might come to learn only pertains to how God has willed to rule. But as soon as unrest begins, the cause for it is due to your unwillingness to obey, your unwillingness to surrender yourself to God.
When there is suffering, but also obedience in suffering, then you are being educated for eternity. Then there will be no impatient hankering in your soul, no restlessness, neither of sin nor of sorrow. If you will but let it, suffering is the guardian angel who keeps you from slipping out into the fragmentariness of the world; the fragmentariness that seeks to rip apart the soul.