Having come out of Egypt and passed through the Red Sea, the Israelites come to Marah, where the water is bitter, they complain, and God shows Moses a piece of wood for the healing of the waters. There follows God’s exhortation: if they follow God, “I will not bring on you any of the diseases I brought on the Egyptians, for I am the Lord who heals you.” Immediately thereafter they reach Elim, where there are springs and palm trees, a pleasant place where the water is immediately drinkable.
I assume that “the diseases I brought on the Egyptians” refers primarily to the plagues, which the Israelites had witnessed. So this is mainly a promise that the judgements they had seen enacted would not come to them if they followed God. But coming also between the accounts of the two water places, it is also a powerful promise that God will protect, keep and heal even when the circumstances of life seem adverse. Presumably if the Israelites had not complained at Marah, God would either have altered the water without their asking, or the bitter water would not have harmed them. But God graciously did give them water they found palatable, and then brought them to a place of luxury where they had more water than they needed. Unfortunately, the lesson was not learned, as we next see them complaining about food. After Marah, they ought to have realised that God would give them what was necessary, and sometimes in abundance.
“I am the Lord who heals you” must still be relevant. I don’t take it in practice to mean that Christians never suffer coughs, colds or cancer. We have our Marahs. But we must never view them as signs of God’s judgement. They are not the Egyptian diseases, and God is still our God through them. I believe firmly in supernatural healing and often pray for it when people are ill. But I must also believe that for every time God leads to an Elim (place of joy, health and abundance), there may also be a Marah on the way, where we must trust that God is still healing, providing and working for our good.