ते तं भुक्त्वा स्वर्गलोकं विशालंक्षीणे पुण्य मर्त्यलोकं विशन्ति।
एवं त्रयीधर्ममनुप्रपन्ना गतागतं कामकामा लभन्ते ॥
Transliteration
te taṃ bhuktvā svarga-lokaṃ viśālaṃ kṣīṇe puṇye marta-lokaṃ viśanti |
evaṃ trayī-dharmam anuprapannā gatāgataṃ kāmakāmā labhante || 21 ||
Translation
Having enjoyed the vast realm of heaven, they return to the realm of mortals when the fruits of their virtuous act is exhausted. Thus, those taking actions with interested motives[to attain svarga(the heaven)] and seeking enjoyment in accordance to the three Vedas, remain in the repeated cycle of birth and death."
Purport
In earlier Shloka, Bhagvan Shri Krishna explained, how Yajna is the prescribed method for the followers of Vedas. Invariably those who performed Yajna with sincerity attains the abode of devas(deities). They attain svarga Loka or deva Loka. They enjoy all the happiness and live an elevated life.
But the limitation is that Svarga or heaven is not permanent. A person stays in Svarga Loka(or deva Loka) equivalent to the good deeds performed by him. The moment the fruits of his virtuous acts exhausted he has to return back to the mortal world. A person who has performed more good deeds will stay longer, who has performed less will stay lesser in svarga(the heaven).
What next body he is going to acquires again depends upon what kind of Karma he performed before going to svarga. But in all situation, he remains in the cycle of birth and death.
