People say if God did not create human sickness, illness, disease and mental health than the devil created it.

There some reference here..

demons as the causes of illness, including fever (Luke 4:39), leprosy (Luke 5:13), and arthritis (Luke 13:11–16)…….

So every illness and there are thousands of different illness of the human body is caused by demon the same with mental health. There are millions of different demons and each demon causes own problem like fever, leprosy, arthritis, stomach pain, kidney stones, cold, flue, different cancers or HIV so on.

God allows the demon to cause it, because it is free will of the demon just like war on earth it free will.

Moderator Note

Preaching is not allowed here, and considering that you never returned to your prophecies thread, you don’t get any benefit of the doubt that you might engage in discussion in this one