Their company is essential for understanding the books. Although some say that Prabhupada has given an explanation in his books, even a cursory reading of them reveals the need for living sadhu sanga. Page after page of his commentary stresses the need for the association of living saints. If we are associating with living saints, naturally we will want to be identified with the one who captures our heart as a disciple. If our heart has been captured by a previous acarya, we should find a living one who feels the same way.
Initiation is more than a mere formality.
It is about the love one feels for a sadhu that creates a bond between him and oneself. It is the happy formalization and announcement of that realtionship, and a comittment to it in which 'divya jnana' is transmitted. Previous to Bhaktisiddhanta, at the time of Vaisnava mantra diksa, brahmanas would take off their thread. He introduced the wearing of the thread to make a statement that Vaisnava mantra diksa includes within it whatever was present in the brahmana diksa and brahma gayatri. Our diksa mantras are for awakening the svarupa of the jiva so that he can take full advantage of the liberated Nama and culture his relationship with Krishna.