"A living entity, by constitution, has the propensity to be attached to something. We see that if someone has no object of attachment, if he has no children, then he transfers his attachment to cats and dogs. This indicates that the propensity for attachment cannot be stopped; it must be utilized for the best purpose. Our attachment for material things perpetuates our conditional state, but the same attachment, when transferred to the Supreme Personality of Godhead or His devotee, is the source of liberation.
Here it is recommended that attachment should be transferred to the self-realized devotees, the sādhus. And who is a sādhu? A sādhu is not just an ordinary man with a saffron robe or long beard. A sādhu is described in Bhagavad-gītā as one who unflinchingly engages in devotional service. Even though one is found not to be following the strict rules and regulations of devotional service, if one simply has unflinching faith in Kṛṣṇa, the Supreme Person, he is understood to be a sādhu. Sādhur eva sa mantavyaḥ (BG 9.30). A sādhu is a strict follower of devotional service. It is recommended here that if one at all wants to realize Brahman, or spiritual perfection, his attachment should be transferred to the sādhu, or devotee. Lord Caitanya also confirmed this. Lava-mātra sādhu-saṅge sarva-siddhi haya: (CC Madhya 22.54) simply by a moment’s association with a sādhu, one can attain perfection.
Mahātmā is a synonym of sādhu. It is said that service to a mahātmā, or elevated devotee of the Lord, is dvāram āhur vimukteḥ, the royal road of liberation. Mahat-sevāṁ dvāram āhur vimuktes tamo-dvāraṁ yoṣitāṁ saṅgi-saṅgam (SB 5.5.2). Rendering service to the materialists has the opposite effect. If anyone offers service to a gross materialist, or a person engaged only in sense enjoyment, then by association with such a person the door to hell is opened. The same principle is confirmed here. Attachment to a devotee is attachment to the service of the Lord because if one associates with a sādhu, the result will be that the sādhu will teach him how to become a devotee, a worshiper and a sincere servitor of the Lord. These are the gifts of a sādhu. If we want to associate with a sādhu, we cannot expect him to give us instructions on how to improve our material condition, but he will give us instructions on how to cut the knot of the contamination of material attraction and how to elevate ourselves in devotional service. That is the result of associating with a sādhu."
(Śrīmad-Bhāgavatam 3.25.20, Purport)