You have asked why these people have died, despite reciting supplications and reading prayers of healing for them. Know that these prayers and supplications for healing affect a contingent fate, not a fixed, irrevocable fate. Fate is of two kinds: contingent and irrevocable. An irrevocable fate cannot change or alter. If every sick person someone prays for were healed, no one would leave the elemental form and ascend from this world to the next to progress there because each time someone became sick, supplications would be made and he would be healed. This contradicts the divine and consummate wisdom. Rather, the purpose of asking for healing is to be protected from a contingent fate and to be guarded from a destiny that is not irrevocable. For example, notice that this lamp has a known amount of oil and when it is completely consumed, it will certainly go out. There will be no change or alteration. However, benevolent prayers and asking for healing is the glass that protects the lamp from contrary winds so it is not extinguished by a contingent fate.
`Abdu’l-Baha, excerpted in Muntakhabati az athar hazrat `Abdu’l-Baha, 3:20.