Righteousness

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

Whenever there is a decline in righteousness and an increase in unrighteousness, O Arjuna, at that time I manifest myself on earth.

Paritranaya sadhunam vinashaya cha dushkritam, dharma-samsthapanarthaya sambhavami yuge yuge

To protect the righteous, to annihilate the wicked, and to reestablish the principles of dharma, I appear millennium after millennium.