Other people's explanations usually leave me more befuddled. I do better following my own understanding. His are long and interrelated arguments but following the rules of English as applied to his tale is illuminating.
We need Russia to contain China. China has little in the way of oil resources. They covet Siberia as their northern resource area. Should they have enough of their own oil to break a naval blockade then we all need to bone up on our Mandarin.