'Bhūmi' here names the subtle element of earth, not the gross earth, since the verse says the Nature is divided eightfold. Likewise water, fire, air and ether are named as subtle elements. By 'manas' is meant the cause of the mind, the ego-sense (ahaṃkāra); by 'buddhi', the great principle, the cause of the ego-sense; by 'ahaṃkāra', the unmanifest joined with ignorance. As food mixed with poison is itself called poison, so the unmanifest, the root-cause, bearing the latent trace of the ego-sense, is called the ego-sense, because the ego-sense is what sets things in motion; for in the world it is the ego-sense alone that is seen to be the seed of all activity. This Nature of Mine, as described, My sovereign power of māyā, is divided eightfold.

Of this world, which abides as the manifold blissful things to be enjoyed, the instruments of enjoyment, and the places of enjoyment, this is the matter: know it as Mine, divided eightfold, in the form of earth, water, fire, air, space, and the rest, which have smell and the other qualities, and in the form of the senses, the mind and the rest, and in the form of the great principle and egotism.

This is a brief sub-gloss. For a fuller reading of this verse, see Madhusūdana, Śaṅkara, or Rāmānuja above.

Krishna states the knowledge He promised. The 'I-principle' (ahankara) is itself included within the great principle (mahat).