John Gill Commentary Exodus 15:26

"and he said, If thou wilt diligently hearken to the voice of Jehovah thy God, and wilt do that which is right in his eyes, and wilt give ear to his commandments, and keep all his statutes, I will put none of the diseases upon thee, which I have put upon the Egyptians: for I am Jehovah that healeth thee." — Exodus 15:26 (ASV)

And said, if you will diligently hearken to the voice of the
Lord your God
By this and the following words, they are prepared to expect a body of laws to be given to them, as the rule of their future conduct; and though they were delivered from the rigorous laws, bondage, and oppression of the Egyptians, yet they were not to be without law to God, their King, Lord, and Governor, whose voice they were to hearken to in all things he should direct them:

and will do that which is right in his sight ;
which he shall see and order as fit to be done, and which they were not to dispute or contradict:

and will give ear to his commandments, and keep all his statutes ;
whether moral, ceremonial, or judicial, even all that either had been made known to them, or should be enjoined them hereafter; and this at Mount Sinai, where they received a body of laws, they promised to do; namely, to hear and obey, (Exodus 24:3Exodus 24:7) (Deuteronomy 5:27) .

I will put none of these diseases upon you, which I have brought upon
the Egyptians ;
in any of the plagues inflicted on them, of which they were witnesses; from these they should be preserved, if obedient, but if not, they must expect them, or similar ones, see (Deuteronomy 28:27) ,

for I am the Lord that heals you ;
both in body and soul: in body, by preserving from diseases and curing them when afflicted; and in soul, by pardoning their iniquities, which, in Scripture, is sometimes signified by healing, see (Psalms 103:3) (Malachi 4:2) .