16. Returning to Our Natural Consciousness
apare vasudevasya devakyām yācito 'bhyagāt ajas tvam asya kṣemāya vadhāya ca sura-dviṣām
Others say that since both Vasudeva and Devakī prayed for You, You have taken Your birth as their son. Undoubtedly You are unborn, yet You take Your birth for their welfare and to kill those who are envious of the demigods.
— Śrīmad-Bhāgavatam 1.8.33
It is also said that Vasudeva and Devakī, in their previous birth as Sutapā and Pṛśni, underwent a severe type of penance to get the Lord as their son, and as a result of such austerities the Lord appeared as their son. It is already declared in the  Bhagavad-gītā  that the Lord appears for the welfare of all people in the world and to vanquish the  asuras , or the materialistic atheists.
The Lord says:
yadā yadā hi dharmasya glānir bhavati bhārata
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