Bhagavad Gita Verse 15, Chapter 10

svayamaatmanaatmaanam vettha tvam purushottama |
bhootabhaavana bhootesha devadeva jagatpate || 15 ||
 
Only you yourself know of your true nature, O foremost among all, creator of all beings, lord of all beings and nourisher of this universe.
 
svayam : yourself
aatmanaa : of the true nature of the self
aatmaanam : by the self
vettha : know
tvam : you
purushottama : foremost among all
bhootabhaavana : creator of all beings
bhootesha : lord of all beings
devadeva : lord of all deities
jagatpate : nourisher of the universe
 
Previously, Arjuna said that Ishvara cannot be completely understood through our eyes and ears. But, being eager to still know Ishvara, he began using several words to describe Ishvara in this shloka. He also acknowledges that only Ishvara can know Ishvara, since there was nothing prior to Ishvara. Ishvara is self-evident, just like we do not need another source of light to see the sun.
 
Arjuna addressed Ishvara as “purushottama”, the foremost and eminent person, beyond all cause and effect. He is “bhootabhaavana”, the origin of all beings, the absolute reality that has taken maaya as an upaadhi or qualifier to create this world of names and forms. He is also “bhootesha”, the master and lord of all beings.
 
Even though he is the controller, he is not someone who is a cruel master. He is “devadeva”, the lord of all deities including Indra and Varuna, someone who is revered and adored. Also, Ishvara does not quit once the world is created. He is also “jagatpate”, the protector and nourisher of the universe. However, we need to understand that, like a magician, Ishvara is never affected by the magic show. He is the cause, and the magic show of the universe is the effect.
 
So, if Ishvara can alone know Ishvara, only Ishvara can reveal his glories. Arjuna takes this up next.

Bhagavad Gita Verse 5, Chapter 4

Shree Bhagavaan uvaacha:
bahooni me vyateetaani janmaani tava chaarjuna |
taanyaham veda sarvaani na tvam vettha parantapa || 5 ||
 
Shree Bhagavaan said:
You and I have have undergone many births, O Arjuna. I know all of those (births), but you do not know them, O scorcher-of-foes.
 
bahooni : many
me : mine
vyateetaani : have happened
janmaani : births
tava : your
cha : and
arjuna : Arjuna
taani : those
aham : I
veda : know
sarvaani : all of them
na : do not
tvam : you
vettha : know
parantapa : scorcher-of-foes
 
In this shloka, Shri Krishna begins to reveal his divine nature to Arjuna. Previously, Arjuna raised a doubt as to how did Shri Krishna convey the Gita teaching to the sun. Shri Krishna responds by pointing out the similarity as well as the difference between his birth and Arjuna's birth. The similarity is that both Arjuna and Shri Krishna have taken many births in the past.
 
However, the difference is that Shri Krishna had the knowledge and memory of all his prior births, whereas Arjuna did not. Normally, human beings have such strong identification with their body that it restricts their ability to remember what occurred in another body. We even tend to forget events associated with our own body with the passage of time, including simple things like where we kept our keys in the morning.
 
So if Shri Krishna could recall what happened in all his births, he did not have any identification to his body, and therefore he is not restricted by its limitations. He was speaking as an enlightened being who realized the eternal essence and has dropped identification with his body. But there is more to Shri Krishna than just this aspect. He will reveal more in the next shloka.
 
Footnotes
1. How does the Gita treat the topic of rebirth? Our vaasanaas force us to take a birth in a body. If we chose to use the birth to exhaust those vaasanaas, then the cycle of rebirth is broken. But if we chose to use the birth to accumulate more vaasanaas, then we will be forced to take another birth to exhause the newly acquired vaasanaas. Only by cleansing our vaasanaas can we break the cycle of rebirth or "samsaara".