The indwelling sin of the flesh, as well as, the physical sickness of the body are one and the same. They are both a direct result of the fall of man. Jesus did not come to eradicate sin in the temporal, either in terms of the indwelling sin of the flesh, or physical sickness. He came to give us eternal life. Sin and sickness will not be eradicated until that which is corrupt puts on the incorrupt and is glorified.
When our focus is on sin, we are under the principle of sin, and if we are under the principle of sin, we are under law; for the wages of sin is death, but the gift of God is eternal life in Christ Jesus. This verse does not remove sin from our lives, but rather declares the penalty paid; the fact that death will be swallowed up in life when we are glorified and receive our new heavenly bodies.
What I am saying is this, if our focus is on physical healing with a promise, we are focused on the inherent sin of the physical body which is in a state of corruption. I’m not saying that we should not ask to be healed, however, asking with expectation is an entirely different matter. If Jesus came to eradicate sin and sickness in the temporal, he failed. And since we know Jesus did not fail, what then was His focus; and as a result what then should be ours? What promises can we really hold onto with complete faith? And what promises can we really make to others regarding what Jesus came to provide for mankind?
Remember, that which is not of faith is sin, and sin dwells in the house of bondage with the law.
Footnote: This commentary is mainly directed towards those that hold to a belief system that says since there is no sickness in heaven, there should be no sickness on earth. Or to those that actually promise physical healings to others. This stuff is just plain bad theology; lacking sobriety, as well as a true love and concern for others. If you really love someone, you are not going to make promises to them that may or may not happen.
Subsequent reading: Romans 8:18-25, note esp. verse 23
1 Cor. 15:50-56