The creative energy can make a child. The books teach that it can also make something within you.
Here is the teaching, simply. Every person has a physical body. Every person also has finer layers: a vital layer that keeps the body alive, a layer of emotion and a layer of thought. But the books say that in most people these finer layers are given by nature, loose and borrowed, like clothes handed down. They are not yet truly ours.
The tradition teaches that the kept energy, raised day after day, builds new ones: an astral body, a mental body and a body of conscious will. It calls them the solar bodies, because they are made by conscious work rather than handed out by nature.
This is one reason the energy matters so much in this book. Part IV is about the night and the astral body. A person who keeps the energy tends to have clearer nights, and remembers more of what happens there.
You do not need to accept this teaching in order to practice. You can test the near end of it. After a few weeks of keeping the energy, notice whether your dreams are clearer, your attention steadier and your feelings less scattered.
The far end, the books say, is a person truly born within, no longer only nature’s.