अथ यदवोचंस्वः प्रपद्य इत्यृग्वेदं प्रपद्ये यजुर्वेदं प्रपद्ये सामवेदं प्रपद्य इत्येव तदवोचं तदवोचम् ॥ ३.१५.७ ॥
In plain words
And when I said, "I take refuge in svaḥ," what I said was: I take refuge in the Ṛgveda, I take refuge in the Yajurveda, I take refuge in the Sāmaveda — that is what I said.
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
अथ यद्वाच स्व प्रपद्ये इति, ऋग्वेदादीन्प्रपद्ये इत्येव तदवोचमिति । उपरिष्टान्मन्त्रान् जपेत् तत पूर्वोक्तमजर कोश सदिक्वत्स यथावद्व्यात्वा । द्विर्वचनमादरार्थम् ॥
In plain words
Now, when he said 'I take refuge in svaḥ,' what was spoken was precisely 'I take refuge in the Vedas beginning with the Rigveda.' Having properly meditated upon the previously mentioned ageless sheath, one should subsequently murmur the mantras. The repetition of the words is meant to show deep reverence.
Close to the Sanskrit
Now, what [he] spoke as 'I resort to svaḥ'—precisely that I spoke as 'I resort to the Vedas beginning with the Rigveda'. Afterward, having meditated properly on the aforementioned ageless sheath... one should murmur the mantras. The repetition is for the sake of reverence.