The word
tapaḥ
means “to heat up,” e.g. by placing on fire. In the process of purification, metals are heated and melted, so that the impurities may rise to the top and be removed. When gold is placed in the fire, its impurities get burnt and its luster increases. Similarly, the Vedas state
atapta tanurnatadā mośhnute
(Rig Veda 9.83.1)[v3] “Without purifying the body through austerity, one cannot reach the final state of yog.” By sincerely practicing austerity, human beings can uplift and transform their lives from the mundane to the divine. Such austerity should be performed without show, with pure intent, in a peaceable manner, in conformance with the guidance of the spiritual master and the scriptures.
Shree Krishna now classifies such austerity into three categories—of the body, speech, and mind. In this verse, he talks of the austerity of the body. When the body is dedicated to the service of the pure and saintly, and all sense indulgence in general, and sexual indulgence in particular, is eschewed, it is acclaimed as austerity of the body. Such austerity should be done with cleanliness, simplicity, and care for not hurting others. Here, “Brahmins” does not refer to those who consider themselves Brahmins by birth, but to those endowed with
sāttvic
qualities, as described in verse 18.42.