When we keep our association with Krishna, every activity is proper and liberating, but if we disassociate ourselves from the Lord's mercy then like a hand which is severed from the body we become ugly and useless. — In his letter to Hrisikesa, 26th Nov, 1968.
For Financial gain you need finance experts, similarly, For Spiritual gain you need association of devotee.
Pure devotees of Lord are associates of Lord. To associate means to surrender unto them and surrender means to follow their instructions.
One should learn how to associate with the devotees of the Lord by gathering with them to chant the glories of the Lord. This process is most purifying. As devotees thus develop their loving friendship, they feel mutual happiness and satisfaction and by thus encouraging one another they are able to give up material sense grantification, which is the cause of all suffering. — Srimad Bhagavatam, 11.03.30.
In Chaitanya Caritamrta Lord Caitanya says that sadhu-sanga, the association of a great saintly person, is very important, because even if one is not advanced in knowledge, simply by association with a great saintly person one can immediately make considerable advancement in spiritual life.
A devotee should always aspire to live in the association of advanced devotees and engage in the service of the Lord through the parampara system.