If you wish to generate life, you must return the Yang. The returning the Yang method goes to the center of the Qi and blood, fostering the root of the body. If the Yang root is feeble, the children; water and wood, will be insufficient with nothing leftover.（These are the words of Huang Yuanyu 黄元御）
For me, the heart of the ideas behind the Huo Shen Pai is the idea that the life force is warm/Yang. The simple statement that we are cold when we are dead illustrates the life has warmth within it.