There is no doubt that religion had already waned under the onslaught of the Enlightenment but it was Freud who provided the radically new understanding of human nature that made any religious explanation of the whats and whys of our personhood seem naive.
When a child comes in I believe that it's a 'multipersonhood ' and it knows it its consciousness knows it and it has a nuclei in the center of its consciousness that is the repository of all experience and all knowledge. And when you look in the eyes of your baby and you feel this sense that they are an old soul I believe indeed they are.
Very little is needed to make a happy life it is all within yourself in your way of thinking.