Bhagavad Gita Verse 18, Chapter 15

yasmaatksharamateetohamaksharaadaapi choottamaha |
atosmi loke vede cha prathitaha purushottamaha || 18 ||
 
For, I transcend the perishable and also am superior to the imperishable. Therefore, in the world and in the Vedas, I am well known as the foremost person.
 
yasmaat : for
ksharam : perishable
ateetaha : transcend
aham : I
aksharaat : imperishable
api : also
cha : and
uttamaha : superior to
ataha : therefore
asmi : I am
loke : in the world
vede : in Vedas
cha : and
prathitaha : well known
purushottamaha : foremost person
 
Now, Shri Krishna reveals his true identity as Purushottama, the uttama Purusha, the foremost person, which is a poetic means of referring to the eternal essence, the pure brahman without any limitations. The root of the sanskrit word "uttama" is "ut" or high. This means that there is nothing higher than Purushottama. The imperishable, also known as Prakriti or Maaya, could be considered superior to the perishable world, because Prakriti is the cause and the world is its effect. Any cause is superior than its effect, just like the parents are superior to their children. Since Prakriti exists only as an adhyaasa, a projection on Purushottama, he is greater than anything else.
 
Let us also look at the significance of Purushottama by going deeper into what is meant by cause and effect. According to Vedanta, there are two types of causes. The material cause is the substance which makes the effect. A clay pot is made of clay, so its material cause, its upaadaana kaarana, is clay. But the pot did not make itself. There was an intelligence in the form of a potter that created the clay pot. This is the second type of cause is the nimitta kaarana, known as the intelligent or efficient cause.
 
Some schools of thought assert that the Purushottama is only the intelligent cause and not the material cause. He is like the potter who is distinct and separate than his creation. But in the Advaita school, the Purushottama is not only considered the intelligence behind creation, he is also the raw material behind the creation. The Mundaka Upanishad compares Purushottama to the spider who weaves the web from within himself, and eventually, pulls back the web into himself.
 
We should again not forget that this uttama Purusha, this foremost person, is nothing but our own self, our "I". In fact, uttama Purusha in Sanskrit grammatically means the first person, the "I". He is beyond the perishable tree of samsaara, and also beyond the seed of this tree in the form of Prakriti. What is the result of knowing this uttama Purusha? We will see in the next shloka.