Asad-dharma means referring to the body, karma-kāṇḍīya. Karmīs, they are engaged in asad-dharma, not sad-dharma. Because the body is asat. Antavanta ime dehā nityasyoktāḥ śarīriṇaḥ (BG 2.18). Ime deha. This body is antavat, it is to be perishable, therefore asat. Asato mā sad gama, the Vedic injunction is. Don't be addicted to this asat, this bodily comforts of life. Sad-gama: try to revive your eternal life. These are the Vedic injunction. Therefore Bhāgavata says, yasyātma-buddhiḥ kuṇape tridhātuke . . . sa eva go-kharaḥ (SB 10.84.13). Anyone who is accepting this body as self, he is no better than animal. Go-kharaḥ. Go means cow, and kharaḥ means ass.
So the whole Vedic literature is like that—how to get the spirit soul who is now entangled, or encaged, in this material body. That is sad-dharma; that is sanātana-dharma. Sad means sanātana, which exists. Sanātana means eternal. What is sat, that is eternal. What is asat, that is temporary. So these Gosvāmīs, they engaged themself in studying all the different Vedic literatures. Nana-śāstra-vicaraṇaika-nipunau. They are very expert scrutinizingly studying, and it was put in, in his Bhakti-rasāmṛta-sindhu, so many other books also. Why? Sad-dharma-samsthapakau. Sad-dharma. Sad-dharma means spiritual life, not this material . . .
Just like these modern material scientists, they are discovering so many things simply for the comforts of this body, not for any spiritual advancement. Therefore asat. Narottama dāsa Ṭhākura says, sat-saṅga chāḍi' kainu asate vilāsa: "I have given up sat-saṅga, association wherein I can learn about spiritual advancement of life. Asata vilas: I am engaged enjoying this asat, this body." Body means the senses.