Buddhism ignores the sacrifice and the stadia in a priest's life.
The Upanishads retain them, but only to throw them over at the end when one has learned not to need them.

Philosophically there is no place for the ritual in the Upanishad doctrine; but their teachers stood too much under the dominion of the Br[=a]hmanas to ignore the ritual.

They kept it as a means of perfecting the knowledge of what was essential.
So 'by wisdom' it is said 'one gets immortality.' The Spirit develops gradually in man; by means of the mortal he desires the immortal; whereas other animals have only hunger and thirst as a kind of understanding, and they are reborn according to their knowledge as beasts again.

Such is the teaching of another of the Upanishads, the [=A]itareya [=A]ranyaka.
This Upanishad contains some rather striking passages: "Whatever man attains, he desires to go beyond it; if he should reach heaven itself he would desire to go beyond it" (2.3.3.

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