Mantra 9

नैषा तर्केण मतिरापनेया प्रोक्तान्येनैव सुज्ञानाय प्रेष्ठ ।यां त्वमापः सत्यधृतिर्वतासि त्वादृङ्नो भूयान्नचिकेतः प्रष्टा ॥ ९ ॥

In plain words

This understanding is not to be reached by logic; O dearest, it is taught only by another (who is not different from the Self) for right knowledge. Fixed as you are in truth, which you have attained, may there be for us, O Naciketas, one to ask like you.