Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 31
नोद्धवोऽण्वपि मन्न्यूनो यद्गुणैर्नार्दित: प्रभु: ।अतो मद्वयुनं लोकं ग्राहयन्निह तिष्ठतु ॥ ३१ ॥
noddhavo ’ṇv api man-nyūnoyad guṇair nārditaḥ prabhuḥato mad-vayunaṁ lokaṁgrāhayann iha tiṣṭhatu
Uddhava is not inferior to Me in any way because he is never affected by the modes of material nature. Therefore he may remain in this world in order to disseminate specific knowledge of the Personality of Godhead.
The specific qualification for becoming the representative of the Lord is to be unaffected by the material modes of nature. The highest qualification of a person in the material world is to be a brāhmaṇa. But since a brāhmaṇa is in the mode of goodness, to be a brāhmaṇa is not sufficient for becoming a representative of the Lord. One has to transcend the mode of goodness also and be situated in unalloyed goodness, unaffected by any of the qualities of material nature. This stage of transcendental qualification is called śuddha-sattva, or vasudeva, and in this stage the science of God can be realized. As the Lord is not affected by the modes of material nature, so a pure devotee of the Lord is also not affected by the modes of nature. That is the primary qualification for being one with the Lord. A person who is able to attain this transcendental qualification is called jīvan-mukta, or liberated, even though he is apparently in material conditions. This liberation is achieved by one who constantly engages in the transcendental loving service of the Lord. In Bhakti-rasāmṛta-sindhu (1.2.187) it is stated: “Anyone who, by his actions, mind and words, lives only for the transcendental loving service of the Lord, is certainly a liberated soul, even though he may appear to be in a condition of material existence.” Uddhava was in such a transcendental position, and thus he was selected to be the factual representative of the Lord in His bodily absence from the vision of the world. Such a devotee of the Lord is never affected by material strength, intelligence or even renunciation. Such a devotee of the Lord can withstand all onslaughts of material nature, and therefore he is known as gosvāmī. Only such gosvāmīs can penetrate the mysteries of the Lord’s transcendental loving relationships.