It is the heart that God wants us to understand. By understanding the heart, we can understand why we suffer or have joy. As you continue to read the verses, think of how it is related to the heart, that God wants us to understand.
Interpretation:
God is telling us that the illness as guidance given to others to understand the heart, is from God’s love. It is like our love for our children. We protect them from harm, by warning and guiding them.
Heaven's Truths, in Healing the Body 