Whatever is the seed of all beings, I (the Supreme) am all that. No mobile and immobile creation will be there, if it is to be without Me (the Supreme).
Imagine the confidence and clarity with which Krishna speaks of himself as the Self, the one source of all existence, expression and splendour.
The Self, the Supreme, not the body, is the seed of everything and all. Nothing else gives birth to or engenders anything whatsoever anywhere any time. All are sourced by just one seed, the Self, the Supreme.
Krishna emphatically adds the negative proposition, making the final message doubly strong and compulsive.
In the whole Universe, no existence is possible which is not sourced by the Supreme. Every existence, expression, or appearance has the Self alone as its seed. Self is so full and wholesome in every way. To feel that the Self in our limited body is the unlimited Supreme is very difficult. Hence so much of description and delineation to help grasp the infinitude of the Self.