How do the illnesses which Hashem brings upon Yisrael different to those which He brings upon the other nations?
(15,26) “And He said: If you will diligently listen to the voice of Hashem your G-d and that which is right in His eyes you will do, and you will listen to His commandments and observe all His statutes, all the sicknesses which I inflicted upon Egypt I will not inflict upon you, for I am Hashem your healer.”
The gemora in Sanhedrin 101a asks that if when we observe the Torah Hashem will not inflict upon us sickness, why do we need to be healed?
Many answers have been given to this question, but another way of explaining this posuk is according to the gemora Megillah 13b, which teaches that Hashem does not smite Yisrael unless He creates a cure beforehand. But with the other nations He smites them first and then creates for them a cure.
This is the explanation of our posuk: “all the sicknesses that I inflicted upon Egypt” - where I inflicted them before there was a cure, “I will not inflict upon you, because I am Hashem your healer” - beforehand, and I will create a cure before the sickness.