ya ātmāntar-yāmī puruṣa iti so 'syāṁśa-vibhavaḥ
ṣaḍ-aiśvaryaiḥ pūrṇo ya iha bhagavān sa svayam ayaṁ
na caitanyāt krṣṇāj jagati para-tattvaṁ param iha
yat-that which; advaitam-without a second; brahma-the impersonal Brahman; upaniṣadi-in the Upaniṣads; tat-that; api-certainly; asya-His; tanu-bhā-the effulgence of His transcendental body; yaḥ-who; ātmā-the Supersoul; antaḥ-yāmī-indwelling Lord; puruṣaḥ-the supreme enjoyer; iti-thus; saḥ-He; asya-His; aṁśa-vibhavaḥ-expansion of a plenary portion; ṣaṭ-aiśvaryaiḥ-with the six opulences; pūrṇaḥ-full; yaḥ-who; iha-here; bhagavān-the Supreme Personality of Godhead; saḥ-He; svayam-Himself; ayam-this one; na-not; caitanyāt-than Lord Caitanya; kṛṣṇāt-than Lord Kṛṣṇa; jagati-in the world; para-higher; tattvam-truth; param-another; iha-here.
What the Upaniṣads describe as the impersonal Brahman is but the effulgence of His body, and the Lord known as the Supersoul is but His localized plenary portion. He is the Supreme Personality of Godhead, Kṛṣṇa Himself, full with six opulences. He is the Absolute Truth, and no other truth is greater than or equal to Him.
The compilers of the Upaniṣads speak very highly of the impersonal Brahman. The Upaniṣads, which are considered the most elevated portion of the Vedic literature, are meant for persons who desire to get free from material association and who therefore approach a bona fide spiritual master for enlightenment. The prefix upa- indicates that one must receive knowledge about the Absolute Truth from a spiritual master. One who has faith in his spiritual master actually receives transcendental instruction, and as his attachment for material life slackens, he is able to advance on the spiritual path. Knowledge of the transcendental science of the Upaniṣads can free one from the entanglement of existence in the material world, and when thus liberated, one can be elevated to the spiritual kingdom of the Supreme Personality of Godhead by advancement in spiritual life.