After leaving Vrindavan for killing Kansa in Mathura, why didn't Krishna ever go back to Vrindavan, where he was brought up, again? Why didn't he ever meet Sri Radha again?
This is a good question because we all wonder it from time to time. How can Shri Krishna leave Vrindavan and His most beloved Radha and never meet Her again! Was this because He was a cheat (chaliya)? No, it's not. The reason is something different. Even in the scripture (Brahmavaivarta Purana), the same question has been asked:
kathaṃ jagāma mathurāṃ tyaktvā vṛndāvanaṃ vanam
kathaṃ tatyāja gopīśca rādhāṃ prāṇādhikāṃ priyām
yaśodāṃ bāndhavādīṃśca nandaṃ va nandanandanaḥ [BVP - 4.55.15,16]
Why did He go to Mathura leaving Vrindavan? Why did He leave the gopis and Radharani who is dear to Him more than His life? And why did He leave Yasoda, Nanda, His kinsmen and His friends?
The reason is due to the effect of a curse that Sridama had given to Radharani. As per that curse Radharani had to experience one hundred years of separation from Her beloved Krishna. God never lets any form of ego or pride (ahmakar) stay in His devotees. Then how could He have let any ego stay in the mind of Shri Radha, His most beloved, that She was the most special of all?:
darpahā darpadaḥ so'pi sarveṣāṃ sarvadaḥ sadā
babhañja rādhādarpaṃ ca sudāmnaḥ śāpakāraṇāt
prāṇādhikāyā rādhāyā anyeṣāmapi kā kathā [BVP - 4.55.15,16,24]
He is the eternal extinguisher of pride of everyone and He broke the pride of Radha through the curse of Sudama. When He broke the pride of Radha, who is dear to Him more than His life, what to say about others?
So in course of events, Shri Radharani got the curse and got separated from Him for hundred years as Shri Krishna left Vrindavan to never return. However, nobody can say the particular reason why Krishna did what He did. He is the Lord of all and who can know His reasons when even Brahma, Vishnu and Shiva fail to do so? So the scripture says:
durjñeyaṃ tadabhiprāyaṃ ko vā jānāti putraka
yatprabhāvaṃ na jānanti brahmaviṣṇumaheśvarāḥ
kathaṃ jānāmi tacceṣṭāmahaṃ vatsa sumandadhīḥ [BVP - 4.55.14,15]
His intentions are difficult to know. Who knows it son, when whose powers are even unknown to Brahma, Vishnu, and Mahesvara! So how can son a dull-witted like me know His intentions?
Nevertheless, when hundreds of years were over the effect of the curse was gone. So Shri Krishna meets Radharani again at a religious place where the residents of Vraj and the yadavas had gathered to perform some worships. In the Mahabharat, it happens in a place named Prabhasa, in this Purana the place has been referred to as Siddhashrama. Thereafter the worship, Parvati says to Shri Radha:
śrīdāmnaḥ śāpanirmuktā śatavarṣāntare sati
kuruṣva madreṇādya kṛṣṇena saha saṃgamam [BVP - 4.124.51]
O Sati, getting free from the curse of Sridama after hundred years today you unite with Shri Krishna happily.
That night Shri Krishna after taking permission from His father goes to meet Radharani, mother Yasoda, Nanda baba and other relatives:
ityuktā bhagavānkṛṣṇaḥ pitroranumatenaca
jagāma rādhikāsthānaṃ nandaśca gokulam tathā [BVP - 4.126.7]
Thus saying Lord Krishna took the permission from His father and went to the place of Radha, Nanda and where the people of Gokula were.
So Shri Krishna actually met Radharani again after the hundred years of separation was over.
Lord Krishnas message in Bhagvadgeeta is to be practical and not emotional. So Lord himself has set the example for us to follow. He wants us to follow KARMAYOGA. As far as Radha is concerned, it is a myth. Radha came into existance only after Gaudiya bhakti sampraday came into existance. Original scriptures of Krishnacharitra like Srimadbhagvat, Mahabharat or Harivansh do not mention any gopi called Radha in Krishnas life.All these are written by Maharshi Vyas who is the only authority to tell you about the life of Lord Krishna.
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(1) Radha can not be a myth and the explanation you have in above answer is vague. If A is not B that does not mean its always C/D/E. My other points would attempt to throw some light on this.
(2) This site page if you read goes closer to explain the reasons why Krishna never returned back to his childhood place. - http://www.purebhakti.com/teachers/bhakti-discourses-mainmenu-61/19-discourses-2000/205-why-did-krishna-not-return.html
(3) Also Krishna did mention all paths that lead to the one Brahma above all. He did not only explain the Karma but many other paths. Our lives are mix of each and every of those (Gyan, Bhakti and Karma, Dhyan) – Its like high-school, we study all subjects.. its only after maturing enough to pick a major/minor – is you will be on one path. Again the Goal is to reach him – no path is destination.
(4) In above other answers, there are quotes from Puranas which are also written by Lord Vyasa as crux & essence of Vedas/Upanishads but his Son - Lord Shukdev (Shuka) was the most close narrator for our age/yug. Now it is believed that Shukdev was born Sanyasi and had learned all vedas/Gita/Puranas while he was in his mother (Pinjala)'s womb and his Father was Lord Vyasa Himself. He never worn a piece of cloth, etc..
(5) There is one thing with authenticity of these three yug old scriptures. The Bhagavat Purana we have in our age/yug is more popularly narrated by Lord Shukdev told to King Parikshit who was almost the last king of Dwapar and kinda first king of Kaliyug's pre-production phase, if you will.
(6) Raadha is the extreme and perfect pure depiction of love and everytime Lord Shukdev would narrate Raadha, he would get "samadhi" for months..this is truly said for many other Lords and in my knowledge, some modern age devotees observed brief period of trance with Singing/Feeling for Raadha too Deepely. Now King Parikshit had only 7 days before he would die of the Curse.. So Lord Shukdev only narrated the overviews of different paths and the ultimate truth of "Tattvabodh". He did not mention the "Bhakti" path too deeply.
* ~~ This is a view of what I understood from various sources including life experiences, & there may be better explanation/justification out there. *