The subtle body is mind, intelligence and ego. So if we think of Krsna in the mind, always, and if we work intelligently for Krsna, that is mind and intelligence. And if we change our false ego, ego means, "I am." So I am at the present moment thinking, "I am American," "I am Indian," "I am white," "I am black," like that. "I am human being," "I am animal," "I am cat or dog," so many things, "I am." This "I am" has to be changed. I am eternal servant of Krsna. In this way, if you educate or transfer the activities of the subtle body, mind, intelligence, and ego, then, at the time of death, you give up this subtle body, material subtle body, mind, intelligence, and ego, and by your spiritual body you go back to home, back to Godhead. This is called Krsna consciousness movement. Gross body, automatically we give up. Now, we should practice to give up the subtle body. To give up this subtle body, one has to develop love for God, prema.
Lecture on Srimad-Bhagavatam 1.2.8, New Vrindaban, 6 September, 1972