When Krishna is born to Vasudeva and Devaki they are overwhelmed on realising that He is none other than the Supreme Lord. What greater fortune could have befallen them is the predominant feeling they experience at that auspicious moment. The new-born child reveals His divine nature as He shines with extraordinary effulgence and with all the indications of His supremacy. He makes known to them that this fortune is bestowed on them by His grace and is a result of their desire to beget the Lord as their son, said Sri B. Sundarkumar in a discourse.
The Lord tells them that in an earlier era they were a devoted couple, Prishni and Sutapa, who had engaged in severe austerities and penance. They finally had darshan of the Lord and, at that time, the Lord wished to grant them whatever they desired. Though they could have easily obtained Moksha from Him, they wished for a son like the Lord. Since there was no possibility of anyone being similar to Him, He Himself was born as Prishnigarba in accordance to their wish.
Again, when they were Kashyapa and Aditi, the Lord was born to them as Vamana. For the third time the Lord is born to the same couple who are now Vasudeva and Devaki. He reveals His divine form so that they can treat Him with the love and affection of parents and also see Him as the Supreme Lord. He promises that with this constant awareness of the Truth they will be liberated at the end of their lives. In the presence of the Supreme Lord as their child, Devaki and Vasudeva experience varied feelings ranging from fear for safety of the child to security that comes from surrendering to the all powerful Lord.
