tvamaksharam paramam veditavyam tvamasya vishvasya param nidhaanam |
tvamavyayaha shaashvatadharmagoptaa sanaatanastvam purusho mato me || 18 ||

You are the imperishable, supreme (being) to be known. You are the supreme foundation of this universe. You are indivisible, the protector of the eternal law. In my opinion, you are the indivisible person.
tvam : you
aksharam : imperishable
paramam : supreme
veditavyam : to be known
tvam : you
asya : this
vishwasya : of this universe
param : supreme
nidhaanam : foundation
tvam : you
avyayaha : indivisible
shaashvatadharma : eternal law
goptaa : protector
sanaatana : eternal
tvam : you
purushaha : person
mataha : opinion
me : my
This shloka is a beautiful blend of upasaana (worship) and jnyaana (knowledge). Arjuna praises Ishvara’s cosmic form, and also reveals his understanding of the relationship between Ishvara and the eternal essence. It is similar to the relationship between the ocean and water that we have seen several times before.
The ocean is the foundation in which several waves are created, sustained and destroyed. Each of those waves thinks that it is separate from the ocean, and is also aware of its mortality. But the water in the ocean and the water in the wave is the same. It is indivisible, eternal, infinite and imperishable. All waves are subject to the universal laws of gravity – whatever goes up, must come down.
Similarly, Ishvara is the foundation which creates, sustains and dissolves this universe of names and forms. Each being thinks that it is separate from Ishvara, and is trapped in sorrow because of its finitude. It does not realize that it is the dweller or the Purusha, made up of the very same eternal essence that Ishvara is, like the ocean and the wave are made up of water. Also, all beings are subject to the universal law of karma, of actions generating results. Ishvara is praised as the protector of this law.
The Gita repeatedly urges us to discard all sectarian notions we have of Ishvara. Next time, when we prostrate in front of Ishvara in the form of a deity, we should try to think of Ishvara in the form that is described here.