दूरमेते विपरीते विषूची अविद्या या च विद्येति ज्ञाता ।
विद्याभीप्सिनं नचिकेतसं मन्ये न त्वा कामा बहवोऽलोलुपन्त ॥ ४ ॥

dūramete viparīte viṣūcī avidyā yā ca vidyeti jñātā |
vidyābhīpsinaṃ naciketasaṃ manye na tvā kāmā bahavo’lolupanta || 4 ||

4. These two are wide apart, mutually exclusive, leading to different ways, known as ignorance and knowledge. I regard Nachiketas as wishing for knowledge; desires, though numerous, have not shaken thee.

Shankara’s Commentary:

It has been stated that he who, of these pursues the good, attains the good and he that pursues the pleasant forfeits consummation; why is that so? Because, these two travel at a great distance from each-other, being mutually exclusive as they are of the nature of knowledge and ignorance, like light and darkness going different ways, i.e., leading to different results, being the cause of bondage and emancipation. What are these two is explained. Ignorance which, deals with ‘the pleasant’ and knowledge which deals with ‘the good,’ both well understood by the intelligent; here, I regard you Nachiketas, as longings after knowledge, because objects of desire the nymphs and the rest—which tempt the intellect of the ignorant, have not, though numerous, shaken thee, i.e., diverted thee from the path of ‘the good, by creating in you a desire for worldly enjoyment. Therefore, I regards you as longing after knowledge and worthy of attaining ‘the good.’ This is the drift.