The Most famous MAHABHARATA'S Quote

यदा यदा हि धर्मस्य ग्लानिर्भवति भारत ।अभ्युत्थानमधर्मस्य तदात्मानं सृजाम्यहम् ॥

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

"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."

yada--whenever; yada--wherever; hi--certainly; dharmasya--of religion; glanih--discrepancies; bhavati--manifested, becomes; bharata--O descendant of Bharata; abhyutthanam--predominance; adharmasya--of irreligion; tada--at that time; atmanam--self; srjami--manifest; aham.

[JAB JAB DHARTI PE PAAP BARHEGA, JAB-JAB LOG ADHARM KE RASSTE PAR CHALEGA, TAB-TAB VAGAWAN SHRI KRISHNA WILL COME IN THIS WORLD (IN SOME FORM OR OTHER) or INCARNATE HIMSELF TO SAVE THIS WORLD, TO SAVE THE PRIESTS AND TO DESTROY THE EVIL]

Hey Bhaarata (Arjuna). It is Faith which teaches renunciation and is responsible for the elevation and well-being of human beings. Whenever in the passage of time,(yadaa yadaa) Faith (or dharma) is weakened or is under attack, (glaanirbhavati) - and whenever adharma spreads without control (abhyutthaanam.h) - it is then (tadaatmaanM) that I re-incarnate myself (sRRijaamyaham.h) with all my powers to restore Faith.

Whenever there is discrepancies in the discharge of natural laws of God, then God incarnates. Either He incarnates Himself, or He sends His bona fide representative, or He sends His powerful representative, like that. So whenever there is incarnation of God, it is to be understood that there is discrepancies in the matter of discharging the laws made by God. And the laws made by God is called dharma, dharma, or religion. 

So religion, you cannot manufacture; I cannot manufacture. Just like there are so many religions now, manufactured by laymen. Oh, they are not religion. Dharmam tu saksad bhagavat-pranitam: "Dharma means, religion means, which is made by God." Or His representative. Not by anyone. Not that you make a club or association, you manufacture some idea and it becomes religion. No. Dharmam tu saksad bha... Therefore God incarnates. Yada yada hi dharmasya glanir bhavati. Glanir means when there is discrepancies. In that law, which is given by God, when there is discrepancies and people are disturbed, especially the devotees are disturbed, when there is satanic influence, there is, devotees are very much disturbed. So paritranaya sadhunam. When incarnation comes, now, paritranaya sadhunam, the first business is to give protection to the devotees. There is no necessity of God's coming here to settle up things. There is no necessity. He has got omnipotential power. He can do without His presence. But when His devotees become very much disturbed, He comes personally. He comes personally, sends His representative. Paritranaya sadhunam. Sadhunam means devotees. Paritranaya and vinasaya ca duskrtam. And, simultaneously, when He comes, all these miscreants, they are killed. They are annihilated. Vinasaya ca duskrtam. Dharma-samsthapanarthaya, and reestablishing the principle of religion. Yuge yuge sambhavami. The Lord says, "I come in different millenniums." 

It is to demonstrate this truth of the universality of God's perfection and the ideal inclusiveness of everything that this incarnation shone on earth. "Yada yada hi dharmasya glanir bhavati Bharata; Abhyutthanam adharmasya tadatmanam srijamyaham. Paritranaya sadhunam vinasaya cha dushkritam; Dharma-samthapanarthaya sambhavami yuge yuge." "Whenever the balance of the universe is disturbed by external interference from any of its parts, then I reveal Myself as the Power of eternal balancing. For the protection of those who are in harmony, and the rectification of everything disharmonious, I incarnate Myself at every juncture of time." 
Through these verses of the Bhagavad Gita, Sri Krishna proclaims the meaning of his descent for the ascent of the spirit of man. God's incarnation is a perpetual act, an eternal occurrence. It is not merely a historical event that took place centuries back and is not taking place now. The words, 'Yuge yuge', imply every juncture of time. At a great juncture and critical moment and crisis, God manifests Himself to dissolve that crisis and conflict. The perpetual incarnation of God is taking place every moment of time, which is the work of Vishnu, the Sustainer, who is ever vigilant in maintaining the harmony of all creation, which gets disturbed by an excess of rajas and tamas, distracting desires in the direction of objects of sense and torpidity due to excessive fixity caused by dark natures, clouds of unknowing.

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 both 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 Krisna consciousness everywhere.