God's providence over human health reflects His absolute control over both the routine laws of nature and miraculous events. A divine promise establishes a clear connection between the physical well-being of the people and their spiritual state, distinguishing between different types of human suffering.
The primary approach among commentators is that there is a fundamental difference between ordinary sickness and severe disease [רמב״ן, הטור הארוך, רבנו בחיי, מלבי״ם]. Ordinary sickness refers to natural, everyday ailments that arise from climate changes, weather conditions, or poor personal habits like unhealthy diets and exposure to the cold [העמק דבר, רבנו בחיי, מלבי״ם]. Alternatively, this type of illness is understood as a general weakness that spreads through the entire body, forcing a person into bed without localized pain [הכתב והקבלה, אדרת אליהו], or as the physiological breakdown of the body's systems [רש״ר הירש].
Seeking the root cause of all such natural sicknesses, the Sages highlight various factors. These range from the "evil eye," which is viewed as the primary cause of mortality [תורה תמימה, צאינה וראינה, חתם סופר], to environmental elements like wind, cold, and heat, as well as bodily waste. They also point to mental and spiritual burdens, such as anger, heavy worries, and the evil inclination, which tempts a person with temporary sweetness but ends in bitterness [תורה תמימה]. Although God could prevent these natural sicknesses entirely, they sometimes occur to cleanse the people of their sins. However, God promises to remove them swiftly so that they do not disrupt the study of Torah and prayer [שפתי כהן].
In contrast to natural sickness, severe diseases are characterized as localized pain in a specific organ [הכתב והקבלה, אדרת אליהו], the acute sensation of suffering [רש״ר הירש], or a direct physical strike [נתינה לגר]. The specific diseases associated with Egypt refer to unnatural afflictions that arrive as divine punishment [רמב״ן, מלבי״ם], representing an expression of strict justice [רקנאטי]. These include illnesses unique to Egypt, such as leprosy [שד״ל], the actual plagues the Israelites witnessed there [שטיינזלץ], severe judgments like famine, war, and wild beasts [ביאור יש״ר], or even new plagues destined to appear in the future [נחל קדומים].
These severe afflictions are often highly contagious. Yet, a divine promise guarantees that even when God strikes neighboring enemies with such epidemics, the diseases will not infect the Israelites [ספורנו, הכתב והקבלה]. There is a distinct difference in how God handles these two categories of suffering. While He actively removes natural illnesses that occur in the ordinary course of life, He simply does not place miraculous, unnatural plagues upon the people to begin with, as these require His active intervention to exist [מלבי״ם]. This distinction serves to uproot false beliefs in dual powers, proving that God alone controls both the removal of natural hardships and the initiation of miraculous plagues [רלב״ג].
Ultimately, this dynamic serves as both a warning and a promise. If the Israelites observe God's laws, they will be spared, and these severe plagues will be redirected onto their enemies, who are considered enemies of God [רמב״ן, הטור הארוך, ביאור יש״ר]. These foes will suffer the plagues as a precise, measure-for-measure punishment for their malicious thoughts and evil eye directed at the Israelites [חתם סופר]. Furthermore, God goes so far as to alter the very fabric of nature for the Israelites, completely preventing conditions like barrenness. By doing so naturally, He ensures they do not need to rely on miracles, which would otherwise deduct from their spiritual merits [אדרת אליהו (ר׳ יוסף חיים), חתם סופר].