Krishna reveals a striking truth. Every world in creation — even Brahmaloka, the realm of Brahma himself — is subject to return. Go to heaven, go to Indraloka, go even to Brahmaloka — once the accumulated merit runs out, one must come back. Only reaching God brings permanent liberation.
Consider a rented house. No matter how grand or comfortable, there comes a day when you must leave. But your own home is yours forever. In the same way, all the worlds are like rented dwellings. Only God's abode is the permanent home.
Even aspiring to heaven is not the ultimate goal. The final destination is God himself — from whom there is no return.