8. Incarnation is necessary to the double progress, intellectual and moral, that has to be accomplished by a spirit; it ensures its intellectual progress by compelling it to employ its activity in the various pursuits of the earthly life, and it ensures its moral progress by making it feel the need which human beings have for one another. Social life is the touchstone that reveals the good or bad qualities of a spirit. Kindness, malevolence, gentleness, violence, charity, selfishness, generosity, avarice, humility, pride, sincerity, hypocrisy, loyalty, and treachery — in a word, all that constitutes human goodness and human badness — find their motive, aim, and stimulus, in the relations of each human being with his or her fellows. If it were possible for a human being to live alone, he or she would have neither vices nor virtues; for, though isolation may preserve from evil, it also annuls the possibility of goodness.