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ब्रह्मार्पणं ब्रह्म हविर्ब्रह्माग्नौ ब्रह्मणा हुतम् ।
ब्रह्मैव तेन गन्तव्यं ब्रह्मकर्मसमाधिना  ॥

brahmārpaṇaṃ brahma-havir-brahmāgnau brahmaṇā hutam
brahmaiva tena gantavyaṃ brahma-karma-samādhinā – 4.24 

The act of offering is Brahman, the cooked rice offered is Brahman, the fire altar is Brahman, and the offerer too is Brahman. Brahman alone is to be attained by the mind as all activities get merged in Brahman.