jnaanayajnena chaapyanye yajanto  maamupaasate
    ekatwena prithaktwena bahudhaa  vishwatomukham // 9.15 //

Others  again offer the oblation of knowledge and worship Me either as the one with  them or as the distinct from them and still others in various ways worship Me  whose form is the whole universe.

Oblation  of knowledge implies that the knowledge of the Lord is itself a Yajna. The  destruction of ignorance with fires of knowledge is called Gnana Yagna - Wisdom  Sacrifice It implies that for the purpose of invoking Right Knowledge false  ideas in us must be thrown into the flames of Right Knowledge. The Gnana Yagna  has no ritualism. It is a constant attempt on the part of the performer to see  the Consciousness Principle in every familiar name and form in all conditions  and situations. It means an understanding that the Immutable Self pervades all,  holding together the phenomenal multiplicities.

They  offer their worship from the non-dualistic view or from the dualistic view. The  man of realization identifies himself with the All-formed which is the view of  Advaita. Some worship Him by making a distinction between The Lord and  themselves which is the Dualistic view (Dvaita). Some worship Him with the  knowledge that He exists as the various Divinities like Brahma, Vishnu and  Rudra etc (Vishishtaadvaita).

aham kraturaham yajnah  swadhaahamahamaushadham
    mantro’hamahamevajyam ahamagniraham  hutam // 9.16 //

I  am the Kratu, I am the Yajna - the sacrifice, I am the Svadha - the offering  (food) to the ancestors, I am the Aushadha - the medicinal plants and herbs, I  am the Mantra, I am the Ajya - the melted butter (Ghee), I am the fire, and I  am the oblation.

Verses  16 - 19 explain how all the different types of worship performed in variety of  forms become the worship of the one Self - the essence behind the seeming  plurality of the world which is nothing but a superimposition gaining its  existence from the Reality behind it. In this verse the existence of Self  everywhere is explained giving the example of ritualistic worship widely  prevalent in Arjuna's time. He is told that all the methods of worship are  nothing but the worship of the Self.

Not  only the different ritualistic prescriptions (Yajna) are presided over by the  Self but all the vegetable food and medicinal herbs used in the sacrifice  (Aushadha), the ghee poured into the altar of fire (Ajya), the oblations  (Hutam) offered, the fire that is invoked (Agni), the mantras chanted with  which oblation is offered, the food offered to the ancestors (Svadha) and the  Kratu- a kind of Vedic rite are all nothing but the Self expressed in different  ways and through different fields.

The  Vedic sacrifice is interpreted as an offering of our whole nature, an entire self  giving to the Universal Self. What we receive from Him we give back to Him. The  gift and surrender are both His.

Through the symbol of sacrifice the Lord suggests  that He alone forms all the accessories of worship and also the act and the  result of the sacrifice.

pitaahamasya jagato maataa dhaataa  pitaamahah
    vedyam pavitramonkara rik saama yajureva  cha // 9.17 //

I  am the father of this universe - the mother, the sustainer, the grandfather,  the purifier, the knowable, the sacred mono-syllable OM and also the Rig, Sama  and the Yajur Vedas.

In  order to show that the Self permeates everywhere The Lord says that He is the  father, the mother, the sustainer, the grandfather and the purifier of the  worlds. He is the one thing to be known because the Self is that which having  known, everything becomes known. The Self, the substratum of the entire living  universe, is symbolized by the Vedic mantra called OM. Life, which is the flow  of constant experiences, implies the sum-total of all experiences in each one  of us during the waking, dreaming and deep-sleep states.

The  substratum for these three states and their experiences must be something other  than the super-impositions on it just as the container is different from the  contained. The fourth state supporting the ordinary states of consciousness in  every one of us is termed Turiya. The sacred symbol OM represents all these  four states. Therefore the Ultimate indicated by OM is the Self. This Absolute  Reality is the theme of all the Vedas and therefore it is said that ` I am also  the Rik, Sama and Yajus.

gatirbhartaa prabhuh saakshee nivaasah  sharanam suhrit
    prabhavah pralayah sthaanam nidhaanam  beejamavyayam // 9.18 //

I  am the Goal, the Supporter, the Lord, the Witness, the Abode, the Shelter, the  Friend, the Origin, the Dissolution, the Foundation, the Treasure-house and the  Seed which is imperishable.

The  Lord continues the enumeration of Brahman’s various manifestations. He is :

The  Goal (Gati): The Self is the goal because when the imperfections of the world  of multiplicities are crossed over, the Absolute abode of Reality is  experienced.

The  Supporter (Bharta): Just as the desert supports the mirage, the Self lends a  semblance of reality to the varied perceptions of the sense organs and thus  holding together the ever-so-many changes into a consistent pattern which is  called life.

The  Lord (Prabhu): The Self, as the Pure Awareness. is beyond the sorrows and joys  of the apparent and delusory universe just as electric energy is beyond the  characteristics of its own manifestation through varied equipments.

The  Witness (Saakshee): The Self is a mere witness and not a participant as It is  an uninterested illuminator of what is happening in the body, mind and  intellect as well as in the world outside.

The  Abode (Nivasah): When different minds on different occasions project different  forms and moods of a ghost on the same lamp post, the post is said to be the  abode of different ghosts. So too, whenever our sense organs experience the  pluralistic phenomena of the world, the Self or the Awareness is their abode.

The  Shelter (Sharanam): The Self is the refuge or the harbor of tranquility which  protects the confused ego from the sorrows and pains of Samsar.

The  Friend (Suhrith): the Infinite is always the friend of the finite giving the  latter security and well-being.

The  Origin and Dissolution, the Substratum and the Store-house: As mud is in all  pots, gold is in all ornaments, the Self is in the universe. Therefore, all  things can come to manifestation and dissolve into the unmanifest only on the  basis of a substratum. Hence the substratum, the Self, is the store-house of  all names, forms and qualities that constitute the world.

The  Immutable Seed (Beejam Avyayam): In contrast with the other seeds which undergo  changes when they germinate, although the Self is the origin of all beings, It remains  imperishable or unchanged even after beings arise out of it. It is therefore Immutable  i.e. It endures so long as the Samsara endures.

tapaamyahamaham varsham  nigrihnaamyutsrijaami cha
    amritam chaiva mrityushcha sadasacchaaham  arjuna // 9.19 //

As  the sun I give heat; I withhold and send forth the rain; I am immortality and  also death; both being and Non-being, O Arjuna.

This  verse explains that the Self is the essence and the ruling factor behind all  phenomenal objects and happenings in the universe.

I  gave heat: Just as electricity conditioned through various equipments expresses  itself as heat in a heater, light in a bulb and cold in a fridge, the Self, the  Existence itself, identifying with the phenomenon called the sun becomes the  source of heat for the entire universe.

I  withhold and send forth rain: The sun influences the climatic conditions of the  universe thereby causing rainfall or drought.

I  am immortality and also death: Self being the spark of life, It gives realistic  experiences of existence in the world including to the phenomenon called death.  Once it is realized that the Self is Immutable and Eternal, the state of  immortality is reached. Change is what is called death and therefore the Self  is the illuminator of change, Itself ever changeless.

I  am the Being and Non-Being: Sat (existence) and Asat (non-existence) are the  terms used in Vedanta to indicate cause and effect, the manifest and  unmanifest. The Self being that Illuminating factor without which neither  manifest nor unmanifest can be experienced, the Self is conceived of as the  Essence in both the manifest and unmanifest. He is being when manifested and  non-being when the world is unmanifested.

The  main idea is that the devotees regard the Lord in various ways and follow  different methods of worship. The Supreme Lord grants our prayers in whatever  form we worship Him.