"Whatever state of being one remembers when he quits his body, that state he will attain without fail."
At the time of death, the mind and intelligence of a living entity create the subtle form of a certain type of body for the next life. If the mind suddenly thinks of something not very congenial, one has to take a corresponding birth in the next life. On the other hand, if one can think of KRSNa at the time of death, he can be transferred to the spiritual world, Goloka VRndAvana. This process of transmigration is very subtle; therefore SrIla RUpa GosvAmI advises devotees to train their minds in order that they will be unable to remember anything other than KRSNa.
Similarly, the tongue should be trained to speak only of KRSNa and to taste only kRSNa-prasAda. SrIla RUpa GosvAmI further advises, tiSThan vraje: one should live in VRndAvana or any part of VrajabhUmi. VrajabhUmi, or the land of VRndAvana, is supposed to be eighty-four krozas in area. One kroza equals two square miles. When one makes VRndAvana his residence, he should take shelter of an advanced devotee there. In this way one should always think of KRSNa and His pastimes. This is further elucidated by SrIla RUpa GosvAmI in his Bhakti-rasAmRta-sindhu (1.2.294):
kRSNaM smaran janaM cAsya
preSThaM nija-samIhitam
tat-tat-kathA-rataz cAsau
kuryAd vAsaM vraje sadA
"A devotee should always reside in the transcendental realm of Vraja and always engage in kRSNaM smaran janaM cAsya preSTham, the remembrance of SrI KRSNa and His beloved associates. By following in the footsteps of such associates and by entering under their eternal guidance, one can acquire an intense desire to serve the Supreme Personality of Godhead."