As I have said in an earlier post, it was God's justified curse on man for sin which resulted in death and led to decay, infirmity and disease. A reasonable person might assume from that nugget of truth that God's will for fallen humans is that they be ill, at least at times. However, that same God sent his son Jesus to become the curse for us so that we could be freed from its effects. The penalty of death (and with it infirmity, decay and disease) was eradicated by the substitutionary death of the sinless lamb of God.
Since God's wrath against sin was fully expended upon Christ in suffering his passion, none of God's wrath is left for the heirs of salvation. Logically (even if there was no passage like Isaiah 53:4-5), for the sacrifice of Christ to exhaust and expunge the curse of death, it would also, by necessity, wipe out the effects of death, namely, decay, infirmity and disease. Therefore, people who embrace Christ's vicarious sacrifice for sin through faith, should not only have the blessing of sins forgiven and eternal life, but they should also have the provision of healing, now.
The promise of divine health and healing for those within the covenant of faith is well attested in scripture. It is an established pattern, from of old, that clues us into God's management style. He wants those he redeems to be well. That Isaiah makes it clear that healing is provided for within the atonement of Christ only strengthens the point. Some of the last verses of the Apocalypse underline the ultimate intention of God that those that are his be well.
But wait a minute here, we still grow old, get sick and die. Why, if all that I've written above is true? According to the Apostle Paul, these mortal frames formed from Adam and Eve's flesh (genes) must be put off before new bodies untinged by Adam's sin and not subject to death may be put on. We have a very rich inheritance in Christ, but we can only receive a portion of it now while in these dead bodies. We'll have to wait until the resurrection for the full package.
Until then all humanity, even the believing, will continue to die in their time. And while in dying bodies, even Christians can get sick, despite the provision of healing in the atonement. Is there anything that can be done about that? We'll take up that question and the whys and wherefores in the next post on the subject.