dehī nityam avadhyo ‘yaḿ
dehe sarvasya bhārata
tasmāt sarvāṇi bhūtāni
na tvaḿ śocitum arhasi

Translation of Bhagavad Gita 2.30

O descendant of Bharata, he who dwells in the body can never be slain. Therefore you need not grieve for any living being.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

The Lord now concludes the chapter of instruction on the immutable spirit soul. In describing the immortal soul in various ways, Lord Krishna establishes that the soul is immortal and the body is temporary. Therefore Arjuna as a kshatriya should not abandon his duty out of fear that his grandfather and teacher—Bhishma and Drona—will die in the battle. On the authority of Sri Krishna, one has to believe that there is a soul different from the material body, not that there is no such thing as soul, or that living symptoms develop at a certain stage of material maturity resulting from the interaction of chemicals. Though the soul is immortal, violence is not encouraged, but at the time of war it is not discouraged when there is actual need for it. That need must be justified in terms of the sanction of the Lord, and not capriciously.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

“Therefore speak clearly. What should I do and not do? ”

“Do not lament, fight.” In two verses, Krishna explains this.

Commentary by Sri Ramanuja of Sri Sampradaya:

2.30 The self within the body of everyone such as gods etc., must be considered to be eternally imperishable, though the body can be killed. Therefore, all beings from gods to immovable beings, even though they possess different forms, are all uniform and eternal in their nature as described above. The inequality and the perishableness pertain only to the bodies. Therefore, it is not fit for you to feel grief for any of the beings beginning from gods etc., and not merely for Bhisma and such others.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Why then is it seen that even men possessing intelligence lament in this world? It is simply due to ignorance about the true nature of the eternal soul. Having this theme in mind the abstruseness of the eternal soul is being given. One realising the eternal soul by the understanding the truth found within the Vedic scriptures by the words of the spiritual master sees the eternal soul as amazing. One realising the eternal soul as all pervading and of super natural eternity, knowledge and bliss is bewildered and overcome by its incomprehensibility as in the case of something beyond ones capacity to conceive. Another will talk of the eternal soul as amazing and another will hear of the eternal soul as amazing. Others still misguided by erroneous conceptions and overpowered by false doctrines fail to realise the eternal soul even after correctly hearing about it, indicating that even with the opportunity of learning about the eternal soul does not insure that one can understand it fully.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

The eternal soul being a infinitesimal portion of the Supreme Lord is never destroyed even during the repetitious connection and disconnection with the physical body. As this is all in accordance with cosmic order there is certainly no reason to lament for this. The omnipotence of the Supreme Lord is amazing. Another meaning can be it is very rare. Therefore it is amazing when known. The eternal soul being an infinitesimal portion of the Supreme Lord is also amazing and the living entity who is aware of their own eternal soul is also very rare.

Now begins the summation.

What is there to be amazed at for the Supreme Lord to say: It is amazing? Verily what is amazing is the existence of the Supreme Lord Himself. Therefore the spiritually intelligent see the eternal soul as a marvellous expansion of the Supreme Lord and upon realisation of this reality are amazed. Like when the eye sees the expansive sky as being the form of the sky or perceives the expanse of the ocean as being the form of the ocean.

In the Brahma Tarka it is stated thus:

Amazing indeed is the Supreme Lord and it is not possible to find any other comparable to Him. Therefore wisdom about Him is very similar to perceiving Him.

Not being amazed by the Supreme Lord which exists in some is a symptom of those who are spiritually unintelligent. This is indicated by the word kascit meaning some.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

It may be postulated that in regard to the physical body which is actually the transformation of insentient primordial matter that it will merge again into its origins at the end. But such is not the case here. The soul is always referred to as being eternal. This is because it is immutable by nature. The soul is extremely difficult to realise due to its supra- subtlety but it does not become perceptible simply because it is different from the physical body. So the soul is referred to in this verse as being amazing. It is those beings out of millions of beings who by devotion to Lord Krishna have received the mercy to be free from physical attachment and purify their hearts in order to perceive their soul, they see the soul as amazing. In what way is the soul amazing? The soul is more amazing than anything experienced previously because it is transcendent to everything experienced in the material existence. It is not only amazing to the one who perceives the soul as amazing but also to the preceptor who describes the soul as amazing and to the disciple who learns from the preceptor that the soul is amazing as well. There is nothing in material existence that the soul can be compared with. So some others although hearing about the soul are still unable to comprehend it. The understanding is that the perceiver of the soul, the preceptor who describes the soul and the disciple who learns about the soul are all exceedingly difficult to gain association with in life.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

2.30 Because of being partless and eternal, ayam, this dehi, embodied Self; nityam avadhyah, can never be killed, under any condition. That being so, although existing sarvasya dehe, in all bodies, in trees etc., this One cannot be killed on account of Its being allpervasive. Since the indewelling One cannot be killed although the body of everyone of the living beings be killed, tasmat, therefore; tvam, you; na arhasi, ought not; socitum, to grieve; for sarvani bhutani, all (these) beings, for Bhisma and others. Here [i.e. in the earlier verse.] it has been said that, from the standpoint of the supreme Reality, there is no occasion for sorrow or delusion. (This is so) not merely from the standpoint of the supreme Reality, but —

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:    

2.30 Dehi etc. On these grounds, the permanent destruction-lessness of the Self [is established].

Sanskrit Shloka Without Transliteration Marks:

dehi nityam avadhyo ‘yam
dehe sarvasya bharata
tasmat sarvani bhutani
na tvam socitum arhasi

Sanskrit to English Word for Word Meanings:

dehī — the owner of the material body; nityam — eternally; avadhyaḥ — cannot be killed; ayam — this soul; dehe — in the body; sarvasya — of everyone; bhārata — O descendant of Bharata; tasmāt — therefore; sarvāṇi — all; bhūtāni — living entities (that are born); na — never; tvam — you; śocitum — to lament; arhasi — deserve.