What is the sacrifice? Sacrifice means yajnarthe karma. Just at the present moment our conception is that I am the proprietor of everything. Actually, I am not the proprietor. The Isopanisad says that isavasyam idam sarvam: [Iso mantra 1] "The Supreme Lord, Personality of Godhead, or Krsna, He is the proprietor." But deluded by the illusory energy of the material existence, we are thinking that "I am the proprietor." Therefore in the scriptures, in Vedic scriptures, sacrifice is recommended. Sacrifice means you give voluntarily. You give voluntarily. Because we have been so much attached to this material proprietorship, that... And without that attachment, there is no possibility of our becoming free from this material entanglement. But that attachment is very difficult to give up. Therefore sacrifice has been recommended, that "You sacrifice."
Lecture on Bhagavad-gita 4.20-24, New York, August 9, 1966