Does a Muslim's belief that the Quran has a self-contained healing and influential power invalidate the belief that ruqyah (exorcism/incantation) does not inherently have an effect, but rather by the decree and permission of Allah the Almighty? And what is the correct belief concerning this matter?

The Qur’an is a cause for healing; through it, Allah removes ailments, and it is a healing and mercy for the believers, but it only increases the wrongdoers in loss, because it is a proof against them. It must be believed that ruqyah with the Qur’an is a cause for healing, and that healing does not occur except by Allah’s permission alone, for He is the Healer. Legal ruqyah is permissible under certain conditions, among them: that it be with the words of Allah or His names and attributes, or with good invocations that do not contradict the Sharia, and that it be in the Arabic language or what its meaning is understood, and that both the one performing ruqyah and the one receiving it believe that ruqyah does not affect by itself, but by Allah’s permission.