Generally, in the Upaniṣads the Supreme Absolute Truth is described in an impersonal way, but the personal aspect of the Absolute Truth is mentioned in the Īśopaniṣad, where, after a description of the all-pervading “hiraṇmayena pātreṇa”,
“O my Lord, sustainer of all that lives, Your real face is covered by Your dazzling effulgence. Kindly remove that covering and exhibit Yourself to Your pure devotee.” (Śrī Īśopaniṣad 15)
The impersonalists do not have the power to go beyond the effulgence of God and arrive at the personality from whom this effulgence is emanating. At the end of the Īśopaniṣad, however, there is a hymn to the Personality of Godhead. It is not that the impersonal Brahman is denied; it is also described, but that Brahman is considered to be the glaring effulgence of the body of Lord Vishnu. It is also stated by Kṛṣṇa in the Bhagavad-gītā (14.27) that the impersonal Brahman rests on Him: brahmaṇo hi pratiṣṭhāham. The Paramātmā, or Supersoul, who is present within the heart of every living entity and within every atom of the universe, is but the partial representation of Lord Vishnu. As the Supreme He is full in six opulences: wealth, fame, strength, beauty, knowledge and renunciation. In short, we should know that He is Kṛṣṇa, God, and that nothing is equal to or greater than Him.
Ref >> Srila Prabhupada Vani.