Shloka 18
Adhyāya 42 — Mahābhūta–Indriya–Adhyātma-Vyavasthā
Brahmā’s Instruction on Elements and Faculties
अत: परं प्रवक्ष्यामि सर्व विविधमिन्द्रियम् । आकाशं प्रथम भूत॑ श्रोत्रमध्यात्ममुच्यते
ataḥ paraṁ pravakṣyāmi sarva-vidham indriyam | ākāśaṁ prathama-bhūtaṁ śrotram adhyātmam ucyate ||
風神ヴァーユは言った。「今より、諸根の体系を、その多様なありさまのままに説き明かそう。虚空（ākāśa）は諸元素の第一と宣せられ、聴覚（耳）はそれに応ずる内なる霊的機能と語られる。」
वायुदेव उवाच
Educational Q&A
The verse begins an adhyātma-style exposition linking the cosmic elements (bhūtas) with corresponding sense faculties (indriyas): ākāśa (space/ether) is presented as the first element, and hearing (śrotra) as its inner correlate—implying that understanding and disciplining the senses is part of spiritual knowledge.
Vāyudeva is speaking and announces a systematic explanation of the senses in their various forms. He starts the sequence by naming ākāśa as the first element and identifying śrotra (hearing) as the corresponding adhyātma (inner/spiritual) faculty.