Or HaChaim on Deuteronomy 7:14/אור החיים על דברים ז׳:י״ד

1ברוך תהיה מכל העמים, "You will be more blessed than all the nations." This can either mean that there will not be a nation which is greater in stature than the Jewish nation, or it could mean: ברוך תהיה, "you will enjoy certain blessings over and beyond those enjoyed by other nations;" what are these blessings? "There will be none amongst you that are barren genetically." Beyond that, "if there is someone amongst you who has become barren through sickness, G'd will remove this sickness from you, etc." It will thus become common knowledge that you have been blessed by the Lord your G'd.

2The words והסיר ה׳ ממך כל חולי, may also be understood in conjunction with Ketuvot 30 "everything is in the hands of heaven with the exception of the common cold." Inasmuch as the common cold is not a sickness decreed upon man as some form of retribution, G'd promises to remove it from Jews who suffer from it. Concerning other maladies which are in the nature of afflictions sent by G'd, the Torah promises that we will not fall victim to them at all if we keep G'd's commandments.

3Our verse also alerts us that one way of becoming aware of G'd's kindness is the fact that He cures Israel of sickness and disease. We should not presume that if we are free from disease this is due to the fact that at certain times it is natural to be in good health, that there simply are no infectious diseases around at such times. To teach us that this is not so the Torah writes that G'd will not put upon us any of the diseases which were rampant in Egypt and of which we were aware. In other words, these diseases occurred in Egypt all the time. If the Israelites are not subject to these diseases this is proof of G'd's special providence; it is not coincidence or a natural phenomenon.

4In addition, G'd assures us that even when He afflicts our enemies with these infectious diseases we will not catch these infections.