Because of his (Nanda Maharaja's) intense love for Krsna, he forgot who Krsna was and could not understand Krsna's potency. Although Krsna is Narayana Himself, Garga Muni did not disclose this

Expressions researched:
"Because of his intense love for Kṛṣṇa, he forgot who Kṛṣṇa was and could not understand Kṛṣṇa's potency. Although Kṛṣṇa is Nārāyaṇa Himself, Garga Muni did not disclose this"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

Because of intense affection, Nanda Mahārāja could not understand Kṛṣṇa as He is. Garga Muni was able to know everything, past, present and future, by studying the Vedas, but Nanda Mahārāja could not understand Kṛṣṇa directly. Because of his intense love for Kṛṣṇa, he forgot who Kṛṣṇa was and could not understand Kṛṣṇa's potency. Although Kṛṣṇa is Nārāyaṇa Himself, Garga Muni did not disclose this. Thus Nanda Mahārāja appreciated the words of Garga Muni, but because of his deep affection he could not understand who Kṛṣṇa was, although Garga Muni had said that Kṛṣṇa's qualities would be exactly like those of Nārāyaṇa.

SB 10.11.57, Translation and Purport

The words of persons in full knowledge of Brahman never become untrue. It is very wonderful that whatever Garga Muni predicted we are now actually experiencing in all detail.

The purpose of human life is indicated in the Brahma-sūtra: athāto brahma jijñāsā. To make one's life perfect—in the past, present and future—one must learn about Brahman. Because of intense affection, Nanda Mahārāja could not understand Kṛṣṇa as He is. Garga Muni was able to know everything, past, present and future, by studying the Vedas, but Nanda Mahārāja could not understand Kṛṣṇa directly. Because of his intense love for Kṛṣṇa, he forgot who Kṛṣṇa was and could not understand Kṛṣṇa's potency. Although Kṛṣṇa is Nārāyaṇa Himself, Garga Muni did not disclose this. Thus Nanda Mahārāja appreciated the words of Garga Muni, but because of his deep affection he could not understand who Kṛṣṇa was, although Garga Muni had said that Kṛṣṇa's qualities would be exactly like those of Nārāyaṇa.