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.
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.
Pure devotees of Lord are associates of Lord. To associate means to surrender unto them and surrender means to follow their instructions.
To chant God's holy name means to associate directly with Him.
In the sun there is great heat and light, and by reflecting the greatness of the sun's light, the moon in night also appears great. Actually the moon is by nature dark ans cold, but in association with sun it has become accepted as great. Hence by association of the Great, one appears great.