If there is a cure for every illness, why are not all people purified?
The hadith says that every illness can be cured, not that there will be no more sick people. A cure only helps the one who accepts it.
The hadith above makes a clear statement. For every illness that God has allowed, there is also a cure. This applies to the body and equally to the soul. Some conclude from this that all people ought to be healthy and purified. Since this is obviously not the case, they see a contradiction.
But the contradiction does not arise from the hadith. It arises from what people read into it. The hadith says that every illness can be cured. It does not say that every sick person will be cured, nor that illness will disappear. Whoever gives it that meaning is putting words into its mouth that are not there.
An everyday example makes this clear. Today there are effective medicines for many illnesses. Yet there are still sick people, because not everyone knows of the remedy, not everyone goes to a doctor, and not everyone takes the medicine as prescribed. The remedy exists, but it only works for the one who uses it.
It is the same with the soul. The Holy Qur’an calls itself a cure for whatever is in the hearts. The second verse above adds that the same message brings mercy to one person and only loss to another who rejects it. The cure is ready. Whether a person is purified depends on whether they accept it.
The message of the hadith is therefore one of hope. No one is so lost that there is no path to improvement for them.