God said, "If you listen carefully to the voice of the Lord your God and do what is right in his eyes, if you pay attention to his commands and keep all his decrees, I will not bring on you any of the diseases I brought on the Egyptians, for I am the Lord, who heals you." (vs 26)
God said this to the Israelites immediately after supernaturally correcting their thirst problem. They had traveled for three days in the desert. They were weary and thirsty, and when they arrived at Marah, they couldn’t drink the water that was there because it was bitter. So God told Moses to throw some wood into the water so it would become potable. (Naturally! Who wouldn’t have thought of making the water sweet with a tree?!)
Then, God tells the people that if they will continue to listen to Him, they will not have any of the diseases that were brought upon the Egyptians. The thing about this word "disease" is that it does not necessarily describe a physical ailment, but an emotional one. The word has shades of "grief" and "regret" in its meaning. So, God is telling His people that, if they trust in Him, their hearts won’t be sick. They won’t be grieved and fearful.
For God is a healer. You see, we find ourselves naturally in a state of fear and worry. Things in this life can easily make us heartsick or heavy with grief. But knowing the wonderful news about who God is, and listening to His voice, calms our fears and eases our sickness. This is why Isaiah said about God, "Surely He has borne our griefs and carried our sorrows." He wants to take those things away from us!
God is a healer. He can heal fear. He can heal grief. He can heal distress. Any situation that looks impossible to us (like being confronted with a bitter water supply) can be solved by Him in ways we can’t even imagine (tossing in a piece of wood will make it drinkable). And God has given us evidence — both in the Bible and also in personal ways throughout our lives — to help us know that we can trust Him fully.
So, what does your heart need healing from? Listen to God’s voice speaking to you. He is a healer.