I don't think this is true of all moral virtues. For example, the virtue of independence is not created through suffering: it is created by the need to rely on one's own judgment and actions. Along with that, there are many evils and sufferings we see daily that teach us no lessons, for example, a two-year-old dying of cancer or a hurricane destroying homes and lives; showing compassion can be commendable. One could argue, well supported by the evidence of post-Holocaust genocides, that humanity has not taken this lesson to heart. God's goal is to create moral individuals and allows evil to teach us moral lessons that we should learn from. Suffering and evil are not necessary conditions for moral development. We can learn morality without being subjected to evil. Likewise, purposely exposing a person to harm to teach him a lesson seems outrageous. Another major problem with this theodicy is that it makes suffering an image. If morality depends on the existence of suffering, then if there were no suffering, then suffering would exist solely to have morality or teach morality.