Sbg 4.7 etradi

English Translation of Ramanuja's Sanskrit Commentary By Swami Adidevananda 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.