Srila Prabhupada- He ( a devotee) should also make friendship with persons who are on an equal level with himself or who have the same understanding that he does. For a devotee, there is no point in making friendships with ordinary persons; he should make friendship with other devotees so that by discussing among themselves, they may elevate one another on the path of spiritual understanding. This is called iṣṭa-goṣṭhī.

(SB 3.29.17p)