"The statement that 'everything is of no reality whatever in His presence' means that God exists whether or not the world exists, whether it has or has not yet been created.
The world's existence in no way conceals the divine presence.
The simplest, most primary, and most undeveloped understanding of the verse 'The world is filled with His glory' is that God's glory permeates everything like the air that fills a room.
A more sophisticated conception of this verse is that 'there is no other than He' —that all reality that is visible to us, with its many aspects, is only He.
For example, some pictures, like those of M. C. Escher, confuse foreground and background.
The more one focuses, the less sure one is whether one is looking at a black image on a white background or vice versa.
A similar question, with several layers of meaning, is whether a letter is defined by the black of the letter itself or by the white that surrounds it.
(In regard to a Torah scroll, this question acquires a halakhic aspect, for its sanctity extends to the parchment itself.)
In general, we experience the world as the foreground and divinity as its background.
But on the level where 'everything is no reality whatever in His presence,' we attempt to see the world differently.
Rather than perceiving the divine in the background, filling all spaces between things, we look at the things of the world as spaces in the midst of divine Being.
Previously, we may have thought of a real world in whose unreachable shadows God dwells.
Now, to the contrary, we consider that the existence of the world is composed of the shadows of the divine reality."
--Rabbi Adin Steinsaltz
From Understanding the Tanya by Rabbi Adin Steinsaltz