Interesting huh. Jesus isn't saying that some illnesses are caused by a belief in the body having the power to create sickness. He is saying that ALL sicknesses of all kinds are produced by believing that the physical level of 'existence' has CAUSAL POWER over your mind.
Essentially, MAGIC, is the belief that something separate from the mind has power to cause the mind. This is the same as being a victim. It's the same as believing things outside of you do things to you. It's the same as the belief that your brother does something to hurt you and that you then demonstrate this is true by showing harm in your body. That is magical. It's a fantasy about how a 'special power' has come along and produced an 'effect' WITHOUT the mind being involved and WITHOUT YOU CAUSING IT.
The reversal of cause and effect is a gross "confusion of the levels". Confusing mind with body. But moreso, confusing the fact that mind is the creator/dreamer with the body which is the created/dream. Such confusion produces 'magical' explanations for why things happen - they don't seem to happen just because YOU had anything to do with it, they seem to happen through some kind of magical mysterious unexplainable 'something' that happens entirely outside your awareness.
Let's reiterate - ALL SICKNESS is caused by a belief in magic. A BELIEF IN magic. That means, every single time we see ourselves as a victim, every time we are irresponsible for our causal power, every time we are disempowered by ourselves, every time we are 'confused' about WHERE THE CAUSE IS (in our mind - GOD is the ultimate cause), that's when sickness is generated.
Sickness then is an attempt to mis-create by using creation against God. It's where we turn around and instead of extending God, we go AGAINST God. We attempt to block God, stop God, attack God, attack the mind, and prevent Him from being the Cause. That produces every physical, emotional or mental illness. ALL of them. Every sickness on the entire planet in the history of mankind AND all animals and creatures AND even that of the earth and air and water and whatever else... *every* form of sickness in the universe, is caused by this 'level confusion'.
We are looking at a 'creation' - the body - the world - and we are attempting to believe that IT has the power to create, to make things happen, that it has its own alien will, and that it can do things to you ON ITS OWN. That is magic. That will result in sickness.
But even moreso, what we're doing here is, we're trying to deny that God is the cause of all creation. It's not just about 'the cause is in my mind'. God is in your mind, or rather, your mind is IN GOD. When we try to deny that God is the Father, that God is the CAUSE or source of everything real, that produces sickness. We are sick because we're blocking the extension of eternal life (creation). We are sick because we don't want love. We are sick because we believe we are separate from God. We are sick because we don't want to love other people unconditionally. When God is not the cause, we're actually saying, the body/world/ego/separation IS GOD. And we worship it. And all its forms. We replace God with the world, and that means we will be sick.
Put God first!