Catherine, Vivekananda is asking us to recognize that it is nature that is playing its game. When we help beggars and the infirm (and most of the time, we find ourselves moving on), it is because we have received some privileges and find ourselves in a position to be of service. His point is not to build up ego as saviors of those who need saving, but to develop gratitude that we found ourselves in a position to help, and in so doing, we opened ourselves up to the greatest lesson of all - that when we help others, we literally and actually, help ourselves. The joy you get when you've made someone's day is indescribable. And you wouldn't, unless someone was in need of help allowing you to play the role of helper. Therefore, the gratitude to those who play the role of the needy.