Krsna is so powerful that He can immediately take up all the sins of others and immediately make them right. But when a living entity plays the part on behalf of Krsna, he also takes the responsibility for the sinful activities of his devotees. Therefore to become a guru is not an easy task. He has to take all the poisons and absorb them. So sometimes — because he is not Krsna — sometimes there is some trouble. Therefore Caitanya Mahaprabhu has forbidden, “Don’t make many sisyas, many disciples.” But for preaching work we have to accept many disciples — for expanding preaching — even if we suffer. That’s a fact. The spiritual master has to take the responsibility for all the sinful activities of his disciples. Therefore to make many disciples is a risky job unless one is able to assimilate all the sins.

From: Perfect Questions Perfect Answers, by Srila Prabhupada