To Anone: Also, Krishna is a God by birth. He was born as four-handed Vishnu with auspicious marks on his feet. When Devaki requested Him to take a form of an ordinary child, He did so so that fools like you dont question how God can take birth. Actually God never takes birth, He simply comes and goes at His own will.
Anyway, He killed putana at such a small age when a child doesnt even opens his eyes. And the mercy? Putana immediately achived liberation. Tjough she came to 'so-calle' kill Krishna, but because she feeded milk to Krishna, she achieved liberation. This is God's mercy. Can you give anyone liberation? Are you capable? You are yourself bound by Maya, what you can do except questioning the supernatural inconceivable activities of God?
Krishna says in BG, 'Out of thousands among men, one may endeavour for liberation and out of thousands among those who achived liberation hardly one knows Me in truth'. Krishna purposely plays human liek activities to further illude fools like you.
He says in Bhagvatam 'even if someone sincerely understands and succeds in understanding even one of my lilas out of the millions one, then such a person is sure to get rid of this cycle of birth and death and come back to me'.
