श्रोत्रमेवर्ङ्मनः साम तदेतदेतस्यामृच्यध्यूढंसाम तस्मादृच्यध्यूढंसाम गीयते ।श्रोत्रमेव सा मनोऽमस्तत्साम ॥ १.७.३ ॥
In plain words
The ear is the Ṛc and the mind is the Sāman. This Sāman rests upon that Ṛc; therefore the Sāman is sung as resting upon the Ṛc. The ear is sā and the mind is ama, and that makes sāman.
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
श्रोत्रमेव ऋक् मन साम, श्रोत्रस्याधिष्ठातृत्वान्मनस सामत्वम् ॥
In plain words
The ear is the ṛk and the mind is the sāman. Because the mind presides over the ear, it holds the nature of the sāman.
Close to the Sanskrit
The ear indeed is ṛk, the mind is sāman, because of the mind's being the controller of the ear, there is the sāman-ness.