Exodus 15:25-26
God Heals Us
25 There the LORD made a decree and a law for them, and there he tested them. 26 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."
When God was leading Moses and the Israel's to the promised land, He made a decree and tested them...The Israeli's were on there way from being a group of people to a civilized nation... Their country would be the promised land, the land of milk and honey...The people being led out of Egypt would have been, in a physical sense, very close to God...The people did not always pay attention to God and His commands...They would be in the desert for forty years, before becoming a nation...The people needed this long to learn the law and the tests that God would provide...
God in verse 26 above says the Lord is the one who heals us...Our Father gave us an immune system to fight infections and viruses, and doctors to treat our illnesses...But God is the one who heals us...