Regarding Nityananda Prabhu breaking the sannyasi rod of Lord Caitanya, the explanation is that this was to show that Lord Caitanya was Krishna, so He had no necessity of taking sannyasa. In the higher sense the Vaisnavas are meant for being members of the family of Krishna to serve as friend, to serve as parent or to serve as lover. So for such elevated devotees sannyasa is superfluous. But still, Lord Caitanya took sannyasa just to prove it factually that so far as the material conditions are concerned, they must be given up. Without knowing this fact some so-called Vaisnavas have turned to be sahajiya. This means one who takes everything as very easy. All the acaryas, beginning from Lord Buddha, Sankaracarya, Ramanuja, etc., all of them renounced this world. So renunciation is required, but when one makes further progress after renunciation towards spiritual life and enters into the Pastimes of Krishna, then things become perfect. The summary is that sannyasa is renunciation, which is imperative for all. Nityananda’s breaking the sannyasi rod of Caitanya Mahaprabhu was with the purpose to show that Lord Caitanya is transcendental to all material conditions.
From Srila Prabhupada’s letter to: Kapiladev — Tittenhurst 24 October, 1969