Cannot understand sentence in preface to "Old Indian Legends" by Zitkala-Ša

Question

I'm reading the preface to Old Indian Legends by Zitkala-Ša, originally published in 1901. My mother tongue is not English, and I am having some trouble understanding - in detail - what she actually means or refers to in the final sentence of the quoted text below. I include the whole paragraph for context:

The old legends of America belong quite as much to the blue-eyed little patriot as to the black-haired aborigine. And when they are grown tall like the wise grown-ups may they not lack interest in a further study of Indian folklore, a study, which so strongly suggests our near kinship with the rest of humanity and points a steady finger toward the great brotherhood of mankind, and by which one is so forcibly impressed with the possible earnestness of life as seen through the teepee door!

Answer 1

...a study, which so strongly suggests our near kinship with the rest of humanity and points a steady finger toward the great brotherhood of mankind, and by which one is so forcibly impressed with the possible earnestness of life as seen through the teepee door!"

Our kinship with the rest of humanity is strongly suggested by the study of Indian folklore; (it is) a study which points a steady finger towards the great brotherhood of mankind, and (a study) by which the possible earnestness of life, as seen through the teepee door, is so forcibly impressed upon one.

When you study Indian folklore, and see the world as if through the eyes of the Indian, you'll be impressed by how earnestly life can be lived.