James exhorts us to pray for sick persons with this promise: "the prayer offered in faith will make the sick person well; the Lord will raise him up" (James 5:15). How can we offer such a prayer in faith when we know of faithful Christians with seriously ill loved ones? Begin by believing that God always answers this prayer too.
Lest you think that I have put God in a box and am proposing to put all doctors out of business, consider the careful wording of the Bible: "And the prayer offered in faith will make the sick person well; the Lord will raise him up. If he has sinned, he will be forgiven. Therefore confess your sins to each others and pray for the other so that you may be healed. The prayer of a righteous man is powerful and effective" (James 5:15-16). In the original language James says literally that the Lord will "save" (sōzō) the sick person and will "raise him up." The Bible uses these words elsewhere to refer to spiritual salvation and resurrection, not simply to physical healing (see Luke 19:10; 1 Cor. 1:21; 6:14; 2 Cor. 4:14; Heb. 7:25)
James makes the spiritual connection even clearer by including the command to confess sins as part of the process of praying for healing. God's ultimate purpose is to secure the eternal health of the one who is sick. Whether the illness is a consequence of unconfessed sin or unhealed disease, the ultimate aim of the healing prayer is the spiritual security of the sick person whom God will "save" and "raise up." Note that James promises not merely the healing of the disease through faithful prayer but also the healing of sin: "If he has sinned, he will be forgiven." James is preeminently concerned about saving (in the spiritual sense) the sick person.
Of course, the Lord can heal physical illness, and most of the time he does. I have not died of the many infections, genetic weaknesses, and accidents that are as typical of my life as they are yours. I have prayed for God to heal those stricken with desease, damaged in crashes, and endangered in delivery. After these prayers God has healed many times. God commands us to pray for the sick, and most of the time he does heal. Every moment that my white corpuscles fend off disease, that my immune system staves off internal collapse, and that my path providentially takes me away from countless unseen catastrophes, God answers prayer for my well-being. God may use the natural processes of our body, the blessed insights of modern medicine, of the miraculous intervention of his Spirit to heal. Each is a blessing of his hand for those who understand that no medicine or miracle benefits us apart from his power.
Praying Backwards: Transform Your Prayer Life by Beginning in Jesus' Name, by Bryan Chapell, pgs. 58-59