SB 10.8.49

jātayor nau mahādeve
 bhuvi viśveśvare harau
bhaktiḥ syāt paramā loke
 yayāñjo durgatiṁ taret
Synonyms: 
jātayoḥ — after we two have taken birth; nau — both husband and wife, Droṇa and Dharā; mahādeve — in the Supreme Person, the Supreme Personality of Godhead; bhuvi — on the earth; viśva-īśvare — in the master of all the planetary systems; harau — in the Supreme Lord; bhaktiḥ — devotional service; syāt — will be spread; paramā — the ultimate goal of life; loke — in the world; yayā — by which; añjaḥ — very easily; durgatim — miserable life; taret — one can avoid and be delivered.
Translation: 
Droṇa and Dharā said: Please permit us to be born on the planet earth so that after our appearance, the Supreme Lord, the Personality of Godhead, the supreme controller and master of all planets, will also appear and spread devotional service, the ultimate goal of life, so that those born in this material world may very easily be delivered from the miserable condition of materialistic life by accepting this devotional service.
Purport: 

This statement by Droṇa clearly indicates that Droṇa and Dharā are the eternal father and mother of Kṛṣṇa. Whenever there is a necessity of Kṛṣṇa’s appearance, Droṇa and Dharā appear first, and then Kṛṣṇa appears. Kṛṣṇa says in Bhagavad-gītā that His birth is not ordinary (janma karma ca me divyam).

ajo ’pi sann avyayātmā
 bhūtānām īśvaro ’pi san
prakṛtiṁ svām adhiṣṭhāya
 sambhavāmy ātma-māyayā

“Although I am unborn and My transcendental body never deteriorates, and although I am the Lord of all sentient beings, I still appear in every millennium in My original transcendental form.” (Bg. 4.6) Before Kṛṣṇa’s appearance, Droṇa and Dharā appear in order to become His father and mother. It is they who appear as Nanda Mahārāja and his wife, Yaśodā. In other words, it is not possible for a sādhana-siddha living being to become the father or mother of Kṛṣṇa, for Kṛṣṇa’s father and mother are already designated. But by following the principles exhibited by Nanda Mahārāja and Yaśodā and their associates, the inhabitants of Vṛndāvana, ordinary living beings may attain such affection as exhibited by Nanda and Yaśodā.

When Droṇa and Dharā were requested to beget children, they chose to come to this world to have the Supreme Personality of Godhead as their son, Kṛṣṇa. Kṛṣṇa’s appearance means paritrāṇāya sādhūnāṁ vināśāya ca duṣkṛtām — the devotees are protected, and the miscreants are vanquished. Whenever Kṛṣṇa comes, He distributes the highest goal of life, devotional service. He appears as Caitanya Mahāprabhu for the same purpose because unless one comes to devotional service, one cannot be delivered from the miseries of the material world (duḥkhālayam aśāśvatam), where the living beings struggle for existence. The Lord says in Bhagavad-gītā (15.7):

mamaivāṁśo jīva-loke
 jīva-bhūtaḥ sanātanaḥ
manaḥ ṣaṣṭhānīndriyāṇi
 prakṛti-sthāni karṣati

“The living entities in this conditioned world are My eternal, fragmental parts. Because of conditioned life, they are struggling very hard with the six senses, which include the mind.” The living entities are struggling to become happy, but unless they take to the bhakti cult, their happiness is not possible. Kṛṣṇa clearly says:

aśraddadhānāḥ puruṣā
 dharmasyāsya parantapa
aprāpya māṁ nivartante
 mṛtyu-saṁsāra-vartmani

“Those who are not faithful on the path of devotional service cannot attain Me, O conqueror of foes, but return to birth and death in this material world.” (Bg. 9.3)

Foolish persons do not know how risky life is here if one does not follow the instructions of Kṛṣṇa. The Kṛṣṇa consciousness movement, therefore, has been started so that by practicing Kṛṣṇa consciousness one can avoid the risky life of this material existence. There is no question of accepting or not accepting Kṛṣṇa consciousness. It is not optional; it is compulsory. If we do not take to Kṛṣṇa consciousness, our life is very risky. Everything is explained in Bhagavad-gītā. Therefore, to learn how to become free from the miserable condition of material existence, Bhagavad-gītā As It Is is the preliminary study. Then, if one understands Bhagavad-gītā, one can proceed to Śrīmad-Bhāgavatam, and if one advances further, one may study Caitanya-caritāmṛta. We are therefore presenting these invaluable books to the whole world so that people may study them and be happy, being delivered from miserable conditional life.