Sri Aurobindo is systematically taking us through the paradigm established in the Taittiriya Upanishad when the disciple comes to his father and asks to learn the nature of the Brahman, and his father repeatedly sends him away to meditate and realise the truth within himself. He starts with the plane of matter, and determines that matter is the Brahman. The next stage is to recognize that Life-Force is the Brahman. And that is the stage in the progression that we now reach in the current chapter.
“Life, though not the original Reality, is yet a form, a power of it which is missioned here as a creative urge of Matter. Life, therefore, has to be accepted as the means of our activity and the dynamic mould into which we have here to pour the Divine Existence; but it can so be accepted only because it is a form of a Divine Energy which is itself greater than the Life-force. The Life-principle is not the whole foundation and origin of things; its creative working cannot be perfected and sovereignly fulfilled or even find its true movement until it knows itself as an energy of the Divine Being and elevates and subtilises its action into a free channel for the outpourings of the superior Nature.”
Sri Aurobindo, The Life Divine, Book 2, Part 2, Chapter 16, The Integral Knowledge and the Aim of Life; Four Theories of Existence