Lord Nityananda alone possesses the distinctive function of the guru. Nityananda is the servant of God, serving Gaurasundara by the distinctive method of reverential servitude. He is identical with Sri Balarama of Krsna-lila. Sri Balarama is not a chum of Krsna, but His respected elder brother. Individual souls are under the direction of Nityananda. They receive the service of Sri Gaurasundara or Krsna at His hands. Nityananda is the ultimate source of the jiva, and the jiva is a potency of Nityananda. Nityananda and His companions form one of the five groups of the associates of Lord Caitanya, whose distinctive function is that of guru. But Nityananda does not directly instruct in the confidential service of Krsna. Srimati Radhika is the guru of the inner circle of the servants of Krsna. Srimati [Radha], however, accepts the offering of service of only those souls who are especially favored by Nityananda, and are deemed by Him to be fit for Her service. There is, therefore, a most intimate relationship between the function of Nityananda and that of Srimati Radharani.

(Srila Bhaktisiddhanta Sarasvati Thakura, in the Harmonist magazine)