ब्रह्मार्पणं ब्रह्महविर्ब्रह्माग्नौ ब्रह्मणा हुतम्। ब्रह्मैव तेन गन्तव्यं ब्रह्मकर्मसमाधिना ॥

brahmārpaṇaṁ brahma havir brahmāgnau brahmaṇā hutam brahmaiva tena gantavyaṁ brahma-karma-samādhinā

The Eternal the oblation, the Eternal the clarified butter, are offered in the Eternal the fire by the Eternal; unto the Eternal verily shall he go who in his action meditateth wholly upon the Eternal.

In plain words: Krishna describes a fire offering, the old Hindu ritual of pouring melted butter into a sacred fire. He says that everything in it is really the Eternal, meaning God or the ultimate reality: the offering, the butter, the fire, and the one who offers. A person who sees God in everything he does will reach God.