You are a spirit that has a soul that has a body. A theory is that if you have a sickness rooted in the body then you will stay healed. However, if the bodily sickness is rooted in the spirit or the soul then there is a possibility that your body won't stay healed unless the root is dealt with. You can't have something happen in one part of you that the other two parts of you don't experience. For example, if you harbor bitterness, it can manifest as a sickness in your body.