अहं क्रतुरहं यज्ञः स्वधाऽहमहमौषधम्। मंत्रोऽहमहमेवाज्यमहमग्निरहं हुतम् ॥

ahaṁ kratur ahaṁ yajñaḥ svadhāham aham auṣhadham mantro ’ham aham evājyam aham agnir ahaṁ hutam

I the ablation; I the sacrifice; I the ancestral offering; I the fire-giving herb; the mantram I; I also the butter; I the fire; the burnt-offering I;

In plain words: Krishna says he is every part of the fire ritual. He is the act of worship, the offering to the ancestors, the healing herb, the sacred chant called a mantra, the butter poured in, the fire, and the offering itself.