The all-pervading space is inside and outside the jar. Likewise, the eternal, ever-present Brahman, the Supreme Reality, is inside and outside all beings and existences.
Mirror is, after all, a material product, visible, solid, with a shape. Reflectionally alone it is present inside and outside the objects we see within it. But in the visible world around us, made up of pañca-bhūtas, earth, water, air and fire are visible. The fifth bhūta, space, is unlike the other four. It is colourless, shapeless. We are able to think of it only because of the other objects hovering within it. Space surrounds and permeates the other bhūtas.
Likewise, the Sage says, the Supreme Reality, Brahman, is inside and outside the whole world-objects, big and small.
We have no doubt about the existence of space. It is within the endless space that all planets and other celestial bodies are hovering, with their respective trajectories. It is also true that the objects have no source besides space, for their prevalence and properties. Space is the source of all we see and interact with.
Like space, the Self, Consciousness, is also all-pervading. It permeates all the things we experience, which are evidently inside our body, in the expanse of the Self alone.
Keep in mind that the world is but an experience for us. All experiences are inside the body, in the mind, in the Consciousness animating the body. As the ‘I’ is Consciousness, everything in, of and by it is also equally so. Grasp this truth and realize it.