The four sages were impersonalists in the beginning of their spiritual life, but afterwards, by the grace of their father and spiritual master, Brahma, they understood the eternal, spiritual form of the Lord and felt completely satisfied
SB Canto 3
O Lord, we therefore offer our respectful obeisances unto Your eternal form as the Personality of Godhead, which You have so kindly manifested before us. Your supreme, eternal form cannot be seen by unfortunate, less intelligent persons, but we are so much satisfied in our mind and vision to see it.
The four sages were impersonalists in the beginning of their spiritual life, but afterwards, by the grace of their father and spiritual master, Brahmā, they understood the eternal, spiritual form of the Lord and felt completely satisfied. In other words, the transcendentalists who aspire to the impersonal Brahman or localized Paramātmā are not fully satisfied and still hanker for more. Even if they are satisfied in their minds, still, transcendentally, their eyes are not satisfied. But as soon as such persons come to realize the Supreme Personality of Godhead, they are satisfied in all respects. In other words, they become devotees and want to see the form of the Lord continually. It is confirmed in the Brahma-saṁhitā that one who has developed transcendental love of Kṛṣṇa by smearing his eyes with the ointment of love sees constantly the eternal form of the Lord. The particular word used in this connection, anātmanām, signifies those who have no control over the mind and senses and who therefore speculate and want to become one with the Lord. Such persons cannot have the pleasure of seeing the eternal form of the Lord. For the impersonalists and the so-called yogīs, the Lord is always hidden by the curtain of yogamāyā. Bhagavad-gītā says that even when Lord Kṛṣṇa was seen by everyone while He was present on the surface of the earth, the impersonalists and the so-called yogīs could not see Him because they were devoid of devotional eyesight. The theory of the impersonalists and so-called yogīs is that the Supreme Lord assumes a particular form when He comes in touch with māyā, although actually He has no form. This very conception of the impersonalists and so-called yogīs checks them from seeing the Supreme Personality of Godhead as He is. The Lord, therefore, is always beyond the sight of such nondevotees. The four sages felt so much obliged to the Lord that they offered their respectful obeisances unto Him again and again.