I have got now this body, Indian body, and then, next body may be cat's and dog's or demigod's, according to my karma. So the body changes. So sanatana-dharma cannot be applied to this body. Sanatana-dharma means the characteristic of the soul. That is sanatana-dharma, to understand the characteristic of the soul. Krsna is describing here the characteristic of the soul: sanatana. And at the conclusion, He gives you information of the sanatana-dharma. What is that? Sarva-dharman parityajya mam ekam saranam vraja [Bg. 18.66]. This is sanatana-dharma. Krsna is sanatana, I am sanatana, you are sanatana.
Lecture on Bhagavad-gita 2.24, Hyderabad, November 28, 1972