Bhagavad Gita Verse 17, Chapter 15

uttamaha purushastvanyaha paramaatmetyudaahyataha |
yo lokatrayamaavishya bibhartyavyaya eeshvaraha || 17 ||
 
But distinct is that foremost person, spoken of as the supreme self, the imperishable lord, who enters and sustains the three worlds.
 
uttamaha : foremost
purushaha : person
tu : but
anyaha : distinct
paramaatma : supreme self
iti : in this manner
udaahyataha : spoken of
yaha : who
lokatrayam : in three worlds
aavishya : enters
bibharti : sustains
avyayaha : imperishable
eeshvaraha : lord
 
As we saw earlier, a single video game program can create an infinite variety of complex worlds in the computer. Let us now pose the question - what is the core, what is the essence of these complex worlds? What is the purest state of these worlds? We need to peel the layers of an onion, as it were. The worlds are not real, they are created by a computer program. A computer program is not real, it is a series of instructions in a computer’s memory. The instructions are not real, they are modifications of electricity. Ultimately, it is electricity that is creating and sustaining all of the worlds we see in a computer game.
 
Now, what if we pose the question - what is at the core of this world? If we get rid of all the limitations, what the purest state of this world? What is the purest state of our existence? The visible world is not real, because it is created by a play of the gunaas of Prakriti, and is perishable. Prakriti or Maaya is not real, though it is relatively imperishable, because it can be destroyed upon removal of our ignorance. What remains, is the eternal essence on which Maaya projects all its limitations or upaadhis.
 
Similarly, if we mentally remove our upaadhis or limitations, it will go something like this. Our body is a play of the gunaas, it is not real. Beyond the body are the senses and the mind, and they are comprised of gunaas and therefore not real. Beyond the senses and mind lies the eternal essence, untainted by Prakriti, which is the purest form of our “I”. In other words, when we remove all of our upaadhis or limitations, we come to the same eternal essence that is reached when we remove the upaadhis of the visible world.
 
We had seen the identity of our “I” with the eternal essence, of aatman with brahman, in the thirteenth chapter as well. That very same eternal essence, the purest brahman or shuddha brahman is referred to as the imperishable lord in this shloka by Shri Krishna. The three worlds here refer to either heaven, earth and hell, or even our waking, dreaming and sleeping states. The eternal essence enters and sustains all of them, but it is not some remote entity. It is the supreme self, the “I” residing within everyone.

Bhagavad Gita Verse 20, Chapter 11

dyaavaaprathivyoridamantaram hi vyaaptam tvayaikena dishashcha sarvaahaa |
drashtvaadbhutam roopamagram tavedam lokatrayam pravyathitam mahaatman || 20 ||
 
This distance between heaven, earth is and all directions is pervaded only by you alone. Having seen this, your fascinating and terrible form, the three worlds are afraid, O great one.
 
dyaavaaprathivyoho : heaven and earth
idam : this
antaram : distance
hi : only
vyaaptam : pervaded
tvayaa : by you
ekena : one
dishashcha : directions
sarvaahaa : all
drashtvaa : having seen
adbhutam : fascinating
roopam : form
agram : terrible
tava : your
idam : this
lokatrayam : three worlds
pravyathitam : afraid
mahaatman : O great one
 
Nowadays, computers can be trained to recognize objects and faces. They do this by first taking a snapshot of a scene, and then differentiating between what is space is what is not. If they can do this differentiation correctly, they can compare the outlines of the “not-space” with outlines of familiar objects to arrive at a conclusion such as “this is a box” and so on.
 
Our eyes work in pretty much the same way. Whenever they see space, they do three things. First, they separate whatever they see as not-space and call those things “objects”. Next, they send those objects to the mind which uses its memory to say “this is a box and a key”. But in addition to recognizing objects, the mind also automatically adds another thought. Since the box and key are separated by space, they are far away from me and therefore not a part of me.
 
Our minds are conditioned to believe that Ishvara is sitting somewhere far away. He is separated from us by space, by distance. But when Arjuna saw the cosmic form, he realized that space is not different from Ishvara. In fact, Shri Krishna himself said that space is part of his nature in the seventh chapter. Ishvara is not separate and far away from us, he is with us all the time. In fact, he only exists, “ekena”, all alone, by himself. We are not different from him. This is the main point of this shloka. Only by constantly remembering the cosmic form will we truly understand this message.
 
Now, Ishvara’s ugra roopa, his terrible form, slowly replaces his saumya roopa, his pleasant for. For every pleasant experience in the world, there has to be a corresponding unpleasant experience as well. Once you label something as “good”, there will be something “bad” by default. Seeing this frightful form of Ishvara, with fire coming out of all his mouths, all the three worlds were beginning to worry.