Lord Sri Krishna tells:
TEXT 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.
TEXT 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.
TEXT 9: One who knows the transcendental nature of My appearance and activities does not, upon leaving the body, take his birth again in this material world, but attains My eternal abode, O Arjuna.
TEXT 10: Being freed from attachment, fear and anger, being fully absorbed in Me and taking refuge in Me, many, many persons in the past became purified by knowledge of Me - and thus they all attained transcendental love for Me.