All verbal teachings are just to cure an illness. Different illnesses require different cures. This is why sometimes it is said there is only Buddha and sometimes that there is no Buddha. True teachings cure the illness. If the cure works, the teachings are true. If they don’t cure the illness, the teachings are false. True teachings are false it they create opinions. False teachings are true if they destroy delusions. The illness is an illusion anyway, so all the cures are also illusions.