Mundaka-1-2-2-yadā lelāyate

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

Of the various kinds of karma, agnihotra is first explained to show what it is, because it is the first of all karma. How is that to be performed? When the flame moves, the five being well fed by fuel, then in the flame so moving between the portions where quantities of ghee are poured on either side, i.e., in the place called avapasthana one should throw the oblations intending them for the devata. As the same has to be done during many days the plural oblations is used. This karma marga which consists in properly offering the oblations, etc., is the road to the attainment of good worlds but it is not easy to do that properly and the impediments are many.

Links
Various resources on the Mundakopanishad
Upanishad Series – Mundakopanishad Commentary by Swami Chinmayananda