vinasaya ca duskritam
sambhavami yuge yuge
"To protect the pious and to annihilate the miscreants, as well as to reestablish the principles of Dharma, I Myself appear, millennium after millennium."
Yuge yuge = every yug, sambhavami = I [Sri Krishna] am born, sadhunam = for the noble persons', paritranayam= strong protection, vinasaya = total destruction of, duskritam = evil persons, samsthapanarthaya = well establishment of, dharma = righteousness. In the last sloka He said He is born whenever Dharma suffers and here He says He is born every yug. That means there is no fixed time or period after which He is born, but anytime when the Dharma suffers and as frequently as the situation demands. We are born and the result is to expend the accumulated papa/ punya. In that process more papa/ punya are accumulated resulting in rebirths. But the Lord is not born because of past karma nor He is born to expend any karma. In the Krishnavatara He has stolen and uttered lies, which are normally considered as papa. But these are not papa as far as He is concerned as He is the Lord. Only in our lives the law maker is bound by the laws he made. For the Lord these laws do not apply. It does not mean He does not care for these laws and reigns a rule of terror. On the contrary the people live happiest in His rule. Thus there is a great difference between His birth and ours. Who are sadhus? Sadhu also means a simple person. But here it is not that meaning. Here it means a person who follows Vedas, who respects His devotees and who leads a righteous life for the sake of others. He will not distinguish between himself and his enemies. That is he has no enemies and all are lovable. He is sadhu, who can not remain a moment separated from the Lord. The Lord protects such persons. He has no enemies as no one is equal to Him in power. But He considers them as enemies , who hurt and oppress noble people. Such people are destroyed. When good people are protected and bad people are destroyed, Dharma gets reestablished. Swami Ramanuja says, to destroy evil persons He need not get born here and He can as well send His weapons and destroy them. For establishment of Dharma also He need not take avatars. But for the protection of sadhus, He has to necessarily descend on this earth. In the story of Gajendra, He could have commanded the Chakra to kill the crocodile and saved the elephant, without having to be present at the venue. But He had to heed the prayer of the elephant and accept the offering and this was possible only by appearing on the scene.