SB 4.20.38

adṛṣṭāya namaskṛtya
 nṛpaḥ sandarśitātmane
avyaktāya ca devānāṁ
 devāya sva-puraṁ yayau
adṛṣṭāya — unto one who is beyond the purview of material vision; namaḥ-kṛtya — offering obeisances; nṛpaḥ — the King; sandarśita — revealed; ātmane — unto the Supreme Soul; avyaktāya — who is beyond the manifestation of the material world; ca — also; devānām — of the demigods; devāya — unto the Supreme Lord; sva-puram — to his own house; yayau — returned.
King Pṛthu then offered his respectful obeisances unto the Supreme Personality of Godhead, who is the Supreme Lord of all demigods. Although not an object of material vision, the Lord revealed Himself to the sight of Mahārāja Pṛthu. After offering obeisances to the Lord, the King returned to his home.

The Supreme Lord is not visible to material eyes, but when the material senses are inclined to the transcendental loving service of the Lord and are thus purified, the Lord reveals Himself to the vision of the devotee. Avyakta means “unmanifested.” Although the material world is the creation of the Supreme Personality of Godhead, He is unmanifested to material eyes. Mahārāja Pṛthu, however, developed spiritual eyes by his pure devotional service. Here, therefore, the Lord is described as sandarśitātmā, for He reveals Himself to the vision of the devotee, although He is not visible to ordinary eyes.

Thus end the Bhaktivedanta purports of the Fourth Canto, Twentieth Chapter, of the Śrīmad-Bhāgavatam, entitled “Lord Viṣṇu’s Appearance in the Sacrificial Arena of Mahārāja Pṛthu.”