Spiritual growth during incarnations is best facilitated when the incarnating entity is faced with natural law, the workings of the Universe as God designed it. Rainfall and its collection into pools and rivulets, sprouting seeds struggling to push grains of earth aside and then leaning hungrily toward the light, a caterpillar's many legs following one another in turn up and down its long body - all wonders of God's natural world. Pain is simply another facet of this natural world, just as carnivores bringing down prey or the old and weak succumbing to infection. Pain is a signal - to pull away from contact that injures, to slow down and rest, to favor the injury, to stay away from certain sites or foods or circumstances. Pain is designed, by natural evolution, to be self limiting. Severe pain causes a faint, long standing pain causes a lethargic depression, and under natural circumstances the animal in pain does not have long to bear this. It dies.
Enter man, with his rules and regulations. Dying is not allowed. Those in chronic, insoluble pain are restrained, bound to the bed and force fed if need be, and maintained in agonizing pain indefinitely. This frequently presents a situation that flies in the face of what the populace has been told by the religious elite - that a benevolent God is listening to their prayers. Those forced to live in pain and those watching this agony then conclude that they are either being punished or ignored. The problem here is not that God is failing to descend to fix the pain. The problem is that mankind has not learned how to deal with God's natural Universe, one of the lessons during spiritual growth.
Beyond the attitude that pain must be borne, stoically, while the body is being maintained indefinitely, humans also burden themselves with unnecessary pain. The vast majority of the pain experienced by humans, even debilitating, chronic pain - is psychological or psychosomatic, induced by the mind. This is not to say that real inflammation or pressure on nerves might not be physically present. This is to say that the inflammation has been caused by the individuals mental state, anxieties, desire to avoid situations, repressed rage, or lack of consideration for their physical body. One has gas pains but fails to eat roughage. One sprains wobbly joints and tears weak muscles because exercise is seldom fit into the busy schedule. One has lower back pain and ultimately a slipped disk, but fails to tighten the tummy or relax tight back muscles. The list is endless.
Ultimately, dealing with pain must be resolved in the same way that one deals with all other aspects of being alive. Take responsibility for your own life, adjust to the reality of those things you cannot change, and maintain perspective.