I have just two things to say, really, about preaching healing: first, all preaching is preaching healing; second, we preach healing by preaching biblical texts.
All preaching is preaching healing because genuine preaching proclaims the kingdom of God; more, it works to usher in that kingdom. The word of God does that, and that is why we preach and what we preach. Healing happens when the kingdom is proclaimed because in the presence of God, sin, death, and the devil cannot abide. This includes disease in all its shapes and forms, reminders of finitude and foreshadowers of death.
The texts are clear: "Bless the Lord, O my soul...who forgives all your iniquity, who heals all your diseases" (Psalm 103:1-3)—two things or one thing? To the paralytic, whose friends had brought him for healing, Jesus said, "Son, your sins are forgiven"—a response that brought controversy and confusion until Jesus said, "Stand up, take your mat and go to your home" (Mark 2:1-12). Two things or one thing? In the NRSV, Jesus sometimes told people, "Your faith has saved you" (Luke 7:50), while other times he said, "Your faith has made you well" (Luke 17:19); but, of course, in Greek he said just one thing: "Your faith has sôzôed you"—sôzô: to save, rescue, deliver, liberate, bring to salvation, restore to health, heal, cure; all of the above, everything that is included in coming to new life in Christ.
Properly understood, the relation between sickness and sin or between forgiveness and healing that we find so often in biblical texts occurs not because God capriciously chooses to inflict illnesses on some unfortunate miscreants, but because sickness and sin together define everything that has gone wrong—not peccadilloes and hangnails, but the whole mess that God comes to re-create (including, of course, peccadilloes and hangnails). The Bible understands that human acts have consequences—big consequences and little ones, direct and indirect, fair and unfair, personal and environmental—and that God is out to reverse those effects for individual people, for nations and communities, for all creation. That is healing. That is the Christian gospel.
To preach Jesus is to preach healing. In the Bible, Jesus heals not because he happens to be a better shaman than other first-century wandering gurus, but because in him is the kingdom of God. Death, demons, and disease know who Jesus is and flee at his arrival. The entry of Jesus is like turning on a light in a cockroach-infested kitchen. The bugs are out of here! So are the demons, and so is disease.
Preaching is not magic, of course. Every paralytic doesn't immediately get up and walk when we preach Mark 2, just as every nation doesn't immediately disarm when we preach Isaiah 2. But we do announce a breaking in of the kingdom that is real and that has real consequence. To keep things real, we preach healing by preaching biblical texts rather than abstractions and generalities. The gospel is not about spirituality in general, it is about the coming of God in particular, Father, Son, and Holy Spirit; it is not about wellness in general, it is about healing in particular—and we get to the particulars in all their wonderful diversity by staying with biblical texts.
Now, to be sure, things sometimes happen in biblical texts that seem to us "magical"—or at least miraculous. (Not magical, finally, because magic is an achievement of the magician, whereas a miracle is a gift of God.) And many of us, too, have seen miraculous healings—even miraculous cures. Healing can occur, as we know, even when cure does not; but sometimes cure happens, too, and gives us cause to wonder. Taking texts seriously and particularly will prevent us from too quickly spiritualizing God's healing work, divorcing it from human bodies and human communities, from nations, politics and the environment. God is out for it all, and faithful preaching will announce that.
Still, texts occur in context. The most important and most amazing context in the Bible is God's incarnational entry into the world. This changes everything. Now, God does not stay safely distant and zap illness from afar; God enters the scene, sharing and bearing in Christ every illness, every disease, the consequence of every sin.
This changes everything about preaching healing biblically. We cannot promise protection from all harm, since not even the son of God was safe from all harm. We cannot promise freedom from viruses and violence, since not even Jesus was protected from such terrors. Was Jesus ever sick? Would the H1N1 vaccine have been effective in his holy body? If he was truly human, this would have to be true.
We preach healing in the context of incarnation, incarnation that led to the cross. No longer is the greatest good to be preserved from pain and suffering but rather to enter into the lives of others, even, if need be, laying down one's life for them. Healing in Christ is always cruciform. This we understand only by hearing and preaching individual healing stories in the light of the whole biblical story. Such preaching is not magic, but it does transform. It enables people to live now in anticipation of the resurrection, the kingdom that is to come and that even now is breaking in. Such preaching heals.