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In the word of God we have instruction relative to special prayer for the recovery of the sick. But the offering of such prayer is a most solemn act, and should not be entered upon without careful consideration. In many cases of prayer for the healing of the sick, that which is called faith is nothing less than presumption.  {MH 227.2}  

Many persons bring disease upon themselves by their self-indulgence. They have not lived in accordance with natural law or the principles of strict purity. Others have disregarded the laws of health in their habits of eating and drinking, dressing, or working. Often some form of vice is the cause of feebleness of mind or body. Should these persons gain the blessing of health, many of them would continue to pursue the same course of heedless transgression of God's natural and spiritual laws, reasoning that if God heals them in answer to prayer, they are at liberty to continue their unhealthful practices and to indulge perverted appetite without restraint. If God were to work a miracle in restoring these persons to health, He would be encouraging sin.  {MH 227.3}  

It is labor lost to teach people to look to God as a healer of their infirmities, unless they are taught also to lay aside unhealthful practices. In order to receive His blessing in answer to prayer, they must cease to do evil and learn to do well. Their surroundings must be sanitary, their habits of life correct. They must live in harmony with the law of God, both natural and spiritual.  {MH 227.4}