Avatarika
अर्थज्ञानप्रधानत्वादुपनिषद ग्रन्थपाठे यत्नोपरमो मा भू-दिति शीक्षाध्याय आरभ्यते--
In plain words
Because understanding the profound meaning is paramount, and so that weariness may not arise during the recitation of the Upanishadic text, the chapter on phonetics is introduced.
Close to the Sanskrit
Because comprehension of meaning is predominant, so that there may not be fatigue in the recitation of the Upanishad text, the chapter on phonetics is commenced.