...and he shall provide for healing" (Mishpatim 21:19) nitna reshus larofeh lerapos (Bava Kama 85a) - so why did Chizkiyahu Hamelech hide the Sefer Herefuos (Brachos 10b)
Rashi in Pesachim 56a writes that Sefer HaRefuos was hidden because their hearts were not humbled over their illness but were, rather, healed immediately.
Rambam in Peirush Hamishna (Pesachim 4:10) rejects this approach arguing that just as one may not hold back food from the hungry, so too one may not withhold healing from the ill.
Instead, Rambam writes that the book contained remedies that are forbidden to use like the usage of talismans and similar forbidden items.
See Chazon Ish in HaEmunah veHabitachon (5:5) for an in depth discussion of this dispute.
As Rashi explains in ברכות on 10b and in פסחים on 56a:
People would not take the illness as a stimulus to do Teshuva, rather they would immediately look up the cure - and lose the divinely-sent lesson of the illness.