Transient nature of all
Sacrifice means giving up kama (desires), krodha (anger) and lobha (greed).
Man generally identifies himself with the Anatma (non-Self) without realizing his true nature.
The reflection of the sky in a pot of water disappears the moment you pour out the water.
Likewise, when you recognise the transient nature of all that is non-Self and empty yourself of desires,
you get closer to the Atma. Unless you sacrifice desire, anger and greed, you cannot attain divinity.