yadā yadā hi dharmasya
glānir bhavati bhārata
abhyutthānam adharmasya
tadātmānaḿ sṛjāmy aham

Translation of Bhagavad Gita 4.7

Whenever and wherever there is a decline in religious practice, O descendant of Bharata, and a predominant rise of irreligion—at that time I descend Myself.

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

The word srijami is significant herein. Srijami cannot be used in the sense of creation, because, according to the previous verse, there is no creation of the Lord’s form or body, since all of the forms are eternally existent. Therefore, srijami means that the Lord manifests Himself as He is. Although the Lord appears on schedule, namely at the end of the Dvapara-yuga of the twenty-eighth millennium of the seventh Manu in one day of Brahma, He has no obligation to adhere to such rules and regulations, because He is completely free to act in many ways at His will. He therefore appears by His own will whenever there is a predominance of irreligiosity and a disappearance of true religion. Principles of religion are laid down in the Vedas, and any discrepancy in the matter of properly executing the rules of the Vedas makes one irreligious. In the Bhagavatam it is stated that such principles are the laws of the Lord. Only the Lord can manufacture a system of religion. The Vedas are also accepted as originally spoken by the Lord Himself to Brahma, from within his heart. Therefore, the principles of dharma, or religion, are the direct orders of the Supreme Personality of Godhead (dharmam tu sakshad bhagavat-pranitam [SB 6.3.19]). These principles are clearly indicated throughout the Bhagavad-gita. The purpose of the Vedas is to establish such principles under the order of the Supreme Lord, and the Lord directly orders, at the end of the Gita, that the highest principle of religion is to surrender unto Him only, and nothing more. The Vedic principles push one towards complete surrender unto Him; and whenever such principles are disturbed by the demoniac, the Lord appears. From the Bhagavatam we understand that Lord Buddha is the incarnation of Krishna who appeared when materialism was rampant and materialists were using the pretext of the authority of the Vedas. Although there are certain restrictive rules and regulations regarding animal sacrifice for particular purposes in the Vedas, people of demonic tendency still took to animal sacrifice without reference to the Vedic principles. Lord Buddha appeared to stop this nonsense and to establish the Vedic principles of nonviolence. Therefore each and every avatara, or incarnation of the Lord, has a particular mission, and they are all described in the revealed scriptures. No one should be accepted as an avatara unless he is referred to by scriptures. It is not a fact that the Lord appears only on Indian soil. He can manifest Himself anywhere and everywhere, and whenever He desires to appear. In each and every incarnation, He speaks as much about religion as can be understood by the particular people under their particular circumstances. But the mission is the same—to lead people to God consciousness and obedience to the principles of religion. Sometimes He descends personally, and sometimes He sends His bona fide representative in the form of His son, or servant, or Himself in some disguised form.

The principles of the Bhagavad-gita were spoken to Arjuna, and, for that matter, to other highly elevated persons, because he was highly advanced compared to ordinary persons in other parts of the world. Two plus two equals four is a mathematical principle that is true in the beginner’s arithmetic class and in the advanced class as well. Still, there are higher and lower mathematics. In all incarnations of the Lord, therefore, the same principles are taught, but they appear to be higher and lower in varied circumstances. The higher principles of religion begin with the acceptance of the four orders and the four statuses of social life, as will be explained later. The whole purpose of the mission of incarnations is to arouse Krishna consciousness everywhere. Such consciousness is manifest and nonmanifest only under different circumstances.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

When do I appear?” This verse answers.

I appear when I cannot tolerate both the destruction (glani) of dharma and the increase (abhyutthanam) of adharma, in order to reverse   the   situation.   I   create   my   body   (atmanam). Madhusudana Sarasvati says, “I show that body which exists eternally, as if it were created by my energy.”

Commentary by Sri Ramanuja of Sri Sampradaya:

4.7 There is no restriction as to the time of My birth; whenever the Dharma taught by the Vedas that must be observed according to the arrangements of the four stations and the four stages of life declines, and Adharma, its opposite, increases, then I Myself, by My own will and in the manner stated, incarnate Myself. Sri Krsna gives the purpose of His birth.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Anticipating the question of exactly when is it that He manifests Himself, Lord Krishna declares unequivocally beginning with the words yada yada meaning whenever and wherever. Whenever there is a decline in righteous and wherever there is a predominance of unrighteousness.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Sri Madhvacharya did not comment on this sloka.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

So it is accepted that Lord Krishna has no beginning and is immutable and that He instructed Visvavan the demi-god of the sun millenniums before in a past incarnation but a question may arise in regard to the many births. When did all these manifestations take place? Lord Krishna clears up this point beginning with the words yada yada meaning whenever and wherever. This signifies that anytime or anyplace that a decline in righteousness is apparent, being antagonistic and in opposition to divinity, at that time the Supreme Lord manifests Himself. Here the word dharma which means righteousness does not imply ordinary righteousness as applies to the mundane interactions of varnasrama or the position and stages in life. Here dharma applies to the deterioration of bhakti yoga or the science of the individual consciousness attaining communion with the ultimate consciousness by the means of loving devotion. When there is a decline in bhakti yoga and the path of devotion to God is opposed by unrighteous rulers who in ignorance are inimical to love of God then at that time Lord Krishna manifests Himself personally. Thus it is stated by Bhumi the goddess of the Earth in the Brahmavaivarta Purana: The Earth is unable to bear the burden of those greatly sinful persons who are averse to devotion to Lord Krishna and who blaspheme Lord Krishna’s devotees. Lord Krishna has explained in the Srimad Bhagavatam that when sattva guna or the mode of goodness increases then humans naturally will proportionately increase in righteousness and devotion to Him. A person living their life without any devotion to God has wasted there human existence and a person who does not take delight in hearing about the sublime transcendental pastimes of the Suprem Lord Krishna which benefits all living entities has lived their life in vain.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

4.7 O scion of the Bharata dynasty, yada yada hi, whenever; bhavati, there is; a glanih, decline, decrease; dharmasya, of virtue consisting of the duties of castes and stages of life of living beings, which are the means to achieving properity and Liberation; and abhyutthanam, increase, rise; adharmasya, of vice; tada, then; do aham, I; srjami, manifest; atmanam, Myself, through Maya. Why?

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:

yada yada hi dharmasya
glanir bhavati bharata
abhyutthanam adharmasya
tadatmanam srjamy aham

Sanskrit to English Word for Word Meanings:

yadā yadā — whenever and wherever; hi — certainly; dharmasya — of religion; glāniḥ — discrepancies; bhavati — become manifested; bhārata — O descendant of Bharata; abhyutthānam — predominance; adharmasya — of irreligion; tadā — at that time; ātmānam — self; sṛjāmi — manifest; aham — I.