Musar zu Schemot 21:19

Healing - Our sages of blessed memory said on the verse "And heal he will be healed" [shemot 21;19] - from here the Torah gave the permission to doctors to heal. [berakhot 40a] And it is also said [with respect to illnesses] - that they are bad and trustworthy [Deut / devarim 28;59] - that they are "trustworthy" as an emissary / delegate [of heaven] [rashi there] for at the time that they are appointed / delegated [to fall upon a person] - it is decreed upon them that they should only leave on a determined day by the appointed doctor using the prescribed medicine. Our sages have also said "A person should not live in a place where there is no doctor" [sanhedrin 17b]