He 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." (Exodus 15:26)
A promise from God to the Israelites in the wilderness. The key words for them in this verse were- listen carefully....do what is right....pay attention....keep all decrees......
Most of them later on neither listened carefully, nor did what was right, nor paid attention and neither kept his decrees. They suffered as a result. Some of the curses resulting in sicknesses for not keeping God's commands are outlined in Deuteronomy Ch. 28.
The LORD will strike you with wasting disease, with fever and inflammation, with scorching heat and drought, with blight and mildew, which will plague you until you perish. (Deuteronomy 28:22)
The LORD will afflict you with the boils of Egypt and with tumors, festering sores and the itch, from which you cannot be cured. (Deuteronomy 28:27)
The LORD will afflict you with madness, blindness and confusion of mind. (Deuteronomy 28:28)
That's a nerve shattering list...and there's more in that chapter.
The point that God stressed upon the Israelites was- If you obey me, I will not bring on you any of the diseases I brought on the Egyptians, for I am the LORD, who heals you.
Well, He is still the God who heals, whether someone believes it or not. He's not changed...He is the One and Only Unchanging God. Praise the Lord.