Chapter IV Sloka 24

apR[< hiv> aaE [a tm!,
Ev ten gNtVy< kmR smaixna

brahmrpaa brahma havi 
brahmgnau brahma hutam |
brahmaiva tena gantavya 
brahma karma samdhin ( 4|24)||

Brahman is the oblation; Brahman is the melted butter (ghee); by Brahman is the oblation poured into the fire of Brahman; Brahman verily shall be reached by him who always sees Brahman in action.

Commentary:

This is Jnana-Yajna or wisdom-sacrifice where the idea of Brahman is substituted for the ideas of the instrument and other accessories of action, the idea of action itself and of its results. By entertaining such an idea the whole action melts away, as stated in the previous verse (No. 23).
When one attains to the knowledge of the Self or Self-realisation his whole life becomes a wisdom-sacrifice in which the ablation, the melted butter or the offering, the performer of the sacrifice, the action and the goal are all Brahman. He who meditates thus wholly upon Brahman shall verily attain to Brahman.
The sage who has the knowledge of the Self knows that the oblation, the fire, the instrument by which the melted butter is poured into the fire and himself have no existence apart from that of Brahman. He who has realised through direct cognition (Anubhava) that all is Brahman, does no action even if he performs actions. ( Cf . III. 15)