paritrāṇāya sādhūnāḿ
vināśāya ca duṣkṛtām
dharma-saḿsthāpanārthāya
sambhavāmi yuge yuge

Translation of Bhagavad Gita 4.8

To deliver the pious and to annihilate the miscreants, as well as to reestablish the principles of religion, I Myself appear, millennium after millennium.

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

According to Bhagavad-gita, a sadhu (holy man) is a man in Krishna consciousness. A person may appear to be irreligious, but if he has the qualifications of Krishna consciousness wholly and fully, he is to be understood to be a sadhu. And duskritam applies to those who do not care for Krishna consciousness. Such miscreants, or duskritam, are described as foolish and the lowest of mankind, even though they may be decorated with mundane education, whereas a person who is one hundred percent engaged in Krishna consciousness is accepted as a sadhu, even though such a person may be neither learned nor well cultured. As far as the atheistic are concerned, it is not necessary for the Supreme Lord to appear as He is to destroy them, as He did with the demons Ravana and Kamsa. The Lord has many agents who are quite competent to vanquish demons. But the Lord especially descends to appease His unalloyed devotees, who are always harassed by the demoniac. The demon harasses the devotee, even though the latter may happen to be his kin. Although Prahlada Maharaja was the son of Hiranyakasipu, he was nonetheless persecuted by his father; although Devaki, the mother of Krishna, was the sister of Kamsa, she and her husband Vasudeva were persecuted only because Krishna was to be born of them. So Lord Krishna appeared primarily to deliver Devaki, rather than kill Kamsa, but both were performed simultaneously. Therefore it is said here that to deliver the devotee and vanquish the demon miscreants, the Lord appears in different incarnations.

In the Caitanya-caritamrita of Krishnadasa Kaviraja, the following verses (Madhya 20.263–264) summarize these principles of incarnation:

srishti-hetu yei murti prapance avatare
sei ishvara-murti ‘avatara’ nama dhare
mayatita paravyome sabara avasthana
visve avatari’ dhare ‘avatara’ nama

“The avatara, or incarnation of Godhead, descends from the kingdom of God for material manifestation. And the particular form of the Personality of Godhead who so descends is called an incarnation, or avatara. Such incarnations are situated in the spiritual world, the kingdom of God. When they descend to the material creation, they assume the name avatara.”

There are various kinds of avataras, such as purushavataras, gunavataras, lilavataras, shakty-avesha avataras, manvantara-avataras and yugavataras—all appearing on schedule all over the universe. But Lord Krishna is the primeval Lord, the fountainhead of all avataras. Lord Sri Krishna descends for the specific purpose of mitigating the anxieties of the pure devotees, who are very anxious to see Him in His original Vrindavana pastimes. Therefore, the prime purpose of the Krishna avatara is to satisfy His unalloyed devotees.
The Lord says that He incarnates Himself in every millennium. This indicates that He incarnates also in the Age of Kali. As stated in the Srimad-Bhagavatam, the incarnation in the Age of Kali is Lord Caitanya Mahaprabhu, who spread the worship of Krishna by the sankirtana movement (congregational chanting of the holy names) and spread Krishna consciousness throughout India. He predicted that this culture of sankirtana would be broadcast all over the world, from town to town and village to village. Lord Caitanya as the incarnation of Krishna, the Personality of Godhead, is described secretly but not directly in the confidential parts of the revealed scriptures, such as the Upanishads, Mahabharata and Bhagavatam. The devotees of Lord Krishna are very much attracted by the sankirtana movement of Lord Caitanya. This avatara of the Lord does not kill the miscreants, but delivers them by His causeless mercy.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

“But your devotees, the rajarsis and brahmarsis can rectify the destruction of dharma and increase of adharma. Then why is it necessary that you make an appearance?”

“That is true. But I come and perform feats which are very difficult for others to do.” That is expressed in this verse.

I appear for delivering (tranaya) my dedicated devotees (sadhunam) whose hearts are bursting with longing, suffering due to their devotion; for destroying the evil-minded persons like Ravana, Kaihsa and Kesi, who give suffering to my devotees, and who cannot be killed except by me; and for establishing in a firm way, the supreme dharma of meditating on me, worshipping, serving me and singing about me, which cannot be instituted by anyone but me (samsthapanarthaya).

I do this in every yuga in the day of Brahma, or in every kalpa (day of Brahma). In this act, one should not worry that the Lord is being prejudiced in punishing the evil-minded. By killing them, the Lord delivers even those most sinful asuras from samsara, from receiving hellish punishment due to their various sinful actions. The Lord’s punishment in the form of killing should thus be seen as his mercy.

Commentary by Sri Ramanuja of Sri Sampradaya:

4.8 The good are those who follow the Dharma, as defined above. They are the foremost among the Vaisnavas, who have taken refuge in Me. While My name, acts and form are inaccessible to speech and thought, these devotees cannot get support, sustenance etc., for themselves without perceiving Me. They regard even a moment’s time without Me as a thousand Kalpas. They become broken in every limb because of the separation from Me. So I am born from age to age in the forms of gods, men etc., for protecting them by affording them the opportunity to behold My form and acts and to converse with Me. I am born also for the destruction of those who are opposed to such devotees and for the restoration of declining Vedic Dharma, which consists of My worship. The main purpose of incarnation is the revealing of His adorable form, so that all may worship Him. The destruction of the wicked is secondary only. There is no specific restrictions of the Yugas like Krta, Treta etc., for the appearance of Divine Incarnations.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Another question may be postulated. For what purpose does Lord Krishna manifest Himself? Anticipating such a question Lord Krishna responds for the protection of the righteous and virtuous and for the annihilation of the sinful and evil. To uphold the tenants and precepts of righteousness that makes sanatan dharma or eternal righteousness invulnerable. For this reason the Supreme Lord incarnates from age to age on particular occasions. But one should not think that the Supreme Lord is biased against the wicked for it is not so, He being equal to all chastises them in the same way a father chastises his son while raising him as a necessary action to insure his proper development.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Actually there is no mandate that for the protection of the righteous and virtuous Lord Krishna must descend and save them. But by His causeless mercy and in some circumstances for sport He manifests Himself by His own sweet will. In the Rig Veda it is described that this will itself is as an inclination of the Lord. A comparison in human terms it is like the bliss that comes with spontaneous creativity. The Supreme Lord is complete within Himself so there is nothing to be gained for Him by any action; yet and still He still performs unlimited activities. Therefore those expert in bhagavat tattva or knowledge of the Supreme Lord Krishna declare that His impulses are all sublime and transcendental to prakriti or material nature. The word glanir in the previous verse does not mean decline as is often translated but glanir means obscure. If dharma meaning eternal righteous is a perennial principle then it must be devoid of any modification of decline. It has to exist eternally in pristine purity. What happens is that dharma becomes obscure to the masses due to material influences on the mind, agitated by the effects of sense gratification by the onslaught of maya or illusion. When such times arise the purpose of human existence becomes distorted and consequently the activities of humans become more and more degenerated and humans become degraded. At this time the dharma of human beings is said to be glanir or obscured.

Therefore as far as dharma is concerned there is no possibility of their being any decline even as darkness is unable to hide sunlight. However even as large clouds are able to obscure the light of the sun from human vision in the same way non-awareness of the independent supremacy of the Supreme Lord and the human beings total dependency on the Supreme Lord consequently obscures the faith in the Supreme Lord as well as any perception of the Supreme Lord in human beings. So the sense is that glanir is referring to obscurity.

The Supreme Lord Krishna is also designated as Brahman which means eternal in time and dynamic in creativity and is the all pervading luminosity of His effulgence. It is not inert or passive. The word Brahman which is derived from the root brh means to grow, to burst forth which infers constant, continuous creativity, perpetually manifesting. That which is dynamic and creative cannot remain static and passive. The dynamic, spontaneous, creative impulse is what is known as the Supreme Lord Krishna’s lila or divine pastimes. The complete material creation and all its embodied beings is the result of one such impulse of the Supreme Lord Krishna and this is also known as lila. The reality of Lord Krishna’s avatars or incarnations such as Rama or Buddha and the understanding of Lord Krishna’s divine lila’s has often been misconstrued and misinterpreted. But here in this verse He explicitly reveals that he comes to protect the righteous and to vanquish the sinful miscreants and to personally re-establish dharma or eternal righteousness.

Sam-sthapana-arthaya- ca infers to establishing one’s true nature. The Lords divine nature assumes His divine form. Because prakriti or material nature is understood as svabhava the word sam has been used referring to that. The word sva also refers Lord Krishna’s essential svarupa or transcendental form as svabhava refers to the innate form or essence and creation is manifested by this essence being the impulse of His will. There is no difference between the form of Krishna and Himself neither is there any difference between the name of Krishna and Himself. In the Narayana Sruti is states that : the Supreme Lord Krishna is immutable yet through the course of creation He manifests Himself in inconceivable many ways in unlimited forms.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

Here the verse reads parittranya sadhunam meaning for protecting the virtuous such protection means specifically for the devotees like Prahlad a great devotee of the Supreme Lord even as a child. His father Hiranyakasipu the demon king was so inimical to devotion to the Supreme Lord that he tried to kill his own son many times but protected by the Supreme Lord, Prahlad was never harmed. Yamaraj the demigod in charge of death who weilds the rod of punishment meted out to the hellish planets; informs his servants to never approach the devotees of the Supreme Lord who behold all with equal vision having taken complete refuge in Him and are under His infallible protection; for neither old age or ourselves are qualified to chastise the devotees in any way. Bring to me those who have never meditated on the Supreme Lord within their heart, bring to me those unrighteous persons of unclean demeanour who do not perform their prescribed duties and bring to me those wretched sinners who are antagonistic and opposed to devotion to the Supreme Lord. So not only does the Supreme Lord Krishna destroys the miscreants but His servitors such as Yamaraj punishes them as well. All this is to enable sanatan dharma or eternal righteousness to be established once again.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

4.8 Paritranaya, for the protection; sadhunam, of the pious, the followers of the virtuous path; vinasaya, for the destruction; duskrtam, of the evil-doers, of the sinful ones; and also dharmasamsthapanarthaya, for establishing virtue fully;-for that purpose, sambhavami, I manifest Myself; yuge yuge, in every age.

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

4.5-9 Bahuni etc. upto Arjuna. Indeed the Bhagavat is Himself devoid of all bodily connections on account of His having the group of the ‘six attributes’ in toto. Yet, out of His nature of stabilising [the universe], and out of compassion, He sends forth (or creates) that is which the Self is secondary. The meaning is this : He takes hold of a body, in which the Self, with the group of ‘six qualities’ in full, remains secondary because of Its role as a helper of the body. On account of this, His birth is divine. For, it has been created not by the results of actions, but by His own Trick-of-Illusion, by the highest knowledge of Yoga, and by the energy of Freedom of His own. His action too is divine, as it is incabable of yielding fruits [for Him]. Whosoever knows this truth in this manner i.e., realises in his own Self also in this manner, he necessarily understands the Bhagavat Vasudeva beng.

Sanskrit Shloka Without Transliteration Marks:

paritranaya sadhunam
vinasaya ca duskrtam
dharma-samsthapanarthaya
sambhavami yuge yuge

Sanskrit to English Word for Word Meanings:

paritrāṇāya — for the deliverance; sādhūnām — of the devotees; vināśāya — for the annihilation; ca — and; duṣkṛtām — of the miscreants; dharma — principles of religion; saḿsthāpana-arthāya — to reestablish; sambhavāmi — I do appear; yuge — millennium; yuge — after millennium.