Very interesting to read especially because it was written early 1900. It promotes the philosophy that every citizen has a duty to be fit and healthy. For protection of yourself, your family and your country. But that this fitness should be only functional.
Hence, it should include basic human skills: running, walking, jumping, climbing, throwing, swimming. But also resilience and cold training. You should always train outside, without shirt (extreme conditions excluded) and every training should contain multiple skills (not only lifting or running).
Of course many parts of this book are outdated. On the other hand it was very refreshing to read about this training philosophy and I for one would have loved it If this was my gym class at school.