Mantra 17

sarvendriyaguṇābhāsaṃ sarvendriyavivarjitaṃ /
sarvasya prabhum īśānaṃ sarvasya śaraṇaṃ suhṛt // 3.17 //

Himself devoid of senses, He shines through the functions of the senses. He is the capable ruler of all; He is the refuge of all. He is great. 

The 1st line of this Mantra occurs in the Bhagavad Gita (13.15) which is quoted below.

sarvendriyagunaabhaasam sarvendriyavivarjitam
asaktam sarvabhricchaiva nirgunam gunabhoktru cha // 13.15 //
Shining by the functions of all the senses, yet without the senses, unattached, yet supporting all, devoid of qualities, yet their experiencer.

The Self in us functioning through the sense organs looks as though It possesses all sense organs. But the sense organs decay and perish while the Consciousness which functions through them and which provides each of them with its own individual faculty is Eternal and Changeless just as electricity is not the light in the bulb and yet when it functions through the bulb it looks as if it were light.

The relationship of refuge or support of all can be explained as follows. Waves are not the ocean but the ocean supports all the waves in as much as there can be no waves without the ocean. Cotton is in the cloth but cloth is not the cotton. But it is the cotton in the cloth that supports the cloth. Similarly the world of plurality is not the Consciousness but it is the Consciousness that supports the world of multiplicities.

The influences which govern the human minds are called Gunas or Qualities. They are Sattwa (Unactivity), Rajas (Activity) and Tamas (Inactivity). A live mind alone can experience these influences. But Life is the illuminator of these influences. Thus Consciousness conditioned by the mind is Jiva, the Ego and that is the experiencer of the Gunas. Unconditioned by the mind, Consciousness in itself is `Its own nature', `It is the Absolute'.

Thus the Self, the Absolute, is beyond sense organs, mind and intellect, detached from everything and without any relation to the various Gunas. But the same Self conditioned by the sense organs looks as though It possess all these sense organs, It is the sustainer of them all and It is the experiencer of all the Gunas.

Hence this Mantra describes the Self as a capable Ruler of all and that He is great. 

Mantra 18

navadvāre pure dehī haṃso lelāyate bahiḥ /
vaśī sarvasya lokasya sthāvarasya carasya ca // 3.18 //

The Swan, the ruler of the whole world, of all that is moving and all that is motionless, becomes the embodied self and dwelling in the city of nine gates, flies outward. 

The Bhagavad Gita says as ubder (5.13)

sarvakarmaani manasaa sannyasyaaste sukham vashee
navadwaare pure dehee naiva kurvan na kaarayan  // 5.13  //
Mentally renouncing all actions and fully subduing his senses, the embodied soul dwells happily in the city of nine-gates, neither acting nor causing others (body and the senses) to act.

This Mantra refers to the Supreme Self as Hamsa, the swan, the destroyer of ignorance. Pervading the universe The Lord appears or becomes the embodied self, the Jiva, and yet He is not affected by the body or other objects in the world just as a swan is not affected by the water in which it swims.

Navadvarepure, the City of nine gates, means the body which has nine apertures in its physical form viz. two eyes, two ears, two nostrils, one mouth, the genital and the excretory outlet without which life cannot be sustained. The Self dwelling within this physical structure flies outward that is to say He activates the instruments of action and perception governing the activities of life though by itself it does not perform any actions. The Self observes the activities around him unaffected, unattached and hence he neither acts nor causes others to act.

Mantra 19

apāṇipādo javano grahītā paśyaty acakṣuḥ sa śṛṇoty akarṇaḥ /
sa vetti vedyaṃ na ca tasyāsti vettā tam āhur agryaṃ puruṣaṃ mahāntam // 3.19 //

Grasping without hands, moving without feet, It sees without eyes, It hears without ears. It knows what is to be known, but no one knows It. They call It the First, the Great, the Full. 

The Lord sees, hears, walks about, and tastes without senses because He enlivens or is  the Consciousness which activates the instruments of action and perception. He is omnipotent and does not depend upon anything else. Hence He is called the First Person, the great and ultimate cause of this universe (agryam purusham  mahāntam).

Mantra 20

aṇor aṇīyān mahato mahīyān ātmā guhāyāṃ nihito 'sya jantoḥ /
tam akratuṃ paśyati vītaśoko dhātuprasādān mahimānam īśam // 3.20 //

The Self, smaller than the small, greater than the great, is hidden in the hearts of creatures. The wise, by the grace of the Creator, behold the Lord, majestic and desireless and become free from grief. 

This whole Mantra occurs in the Kathopanishad also (2.20) where the reference is to Atman instead of Isam.

The Atman is stated to be smaller than a grain of sand and greater than the entire universe. It is the inmost essence of all things that exist, large or small. It gives all things a nature of reality. But by itself it is free from all limitations. The wise ones realize their oneness with the Supreme Self and become free from grief. The Absolute is majestic and desireless because it is free from all upadhis, limitations.

Mantra 21

vedāham etam ajaraṃ purāṇaṃ sarvātmānaṃ sarvagataṃ vibhutvāt /
janmanirodhaṃ pravadanti yasya brahmavādino hi pravadanti nityam // 3.21 //

I know this undecaying, primeval One, the Self of all things, which exists everywhere, being all-pervading and which the wise declare to be free from birth. The teachers of Brahman, indeed, speak of It as eternal.

This chapter is concluded with the statement by the brahmavādin, the teachers of Brahman, paying a bouquet of flowery tributes to the Supreme Purusha as: Ajaram - never aging, Purānam-eternal, Sarvātmānam - the Self of all, Sarvagatam - everywhere and in every being, Vibhutvāt - all pervasive, and Janmanirodham - without birth and death and chanting that the Self is nityam - eternal.

CONCLUSION

This chapter makes out that the Impersonal and the Personal Brahman and Isvara respectively are not two different entities but the same in two aspects.

Iti Svetasvataropanishadi tritiyo’dhyayah ||
HERE ENDS THE THIRD CHAPTER OF THE SVETASVATARA UPANISHAD