"And these are the offspring of Moshe and Aharon on the day that Hashem spoke to Moshe on Har Sinai. These are the names of the sons of Aharon. . ." (Bamidbar 3, 1-2). Rashi notes that although the first pasuk also mentioned the offspring of Moshe, in the subsequent pesukim only the children of Aharon are enumerated. He explains that one who teaches his friend's children Torah is considered as if he begot them. Therefore, Aharon's children are listed as if they were Moshe's offspring, since he taught them Torah.
Rav Wolbe explains that a teacher must be devoted to a student as if he were the teacher's own child. Likewise, a student should perceive his teacher as a parent, as we find Elisha referred to his Rebbi, Eliyahu Hanavi, as "Avi, Avi" - my father, my father. Chazal tell us that he repeated "Avi" a second time because he felt that Eliyahu was not only like a father but also like a mother.
Rav Wolbe related that his Rebbi, Rav Yeruchom Levovitz, once showed Reb Dovid Povarsky a bloody tissue. Rav Yeruchom explained that he had coughed up blood because he was so worried about his son. He had never worried about a student to the extent that he had coughed up blood, and he was therefore concerned that he had not properly fulfilled his obligation as a Rebbi. Despite such a comment, Rav Yeruchom was known to worry greatly about his student's welfare. When one of his students was accused of spying and in great danger, Rav Yeruchom worried so much that when he woke up the next morning his beard had turned white!
Not only did Rav Yeruchom care for his disciples as he cared for his children, his disciples felt as if he was their father. When Rav Wolbe arrived at the Yeshiva in Mir, Poland, he met a student who had been learning in the yeshiva for a few years. The student told Rav Wolbe that he was two years and three months old, because exactly two years and three months ago he met Rav Yeruchom for the first time and was "reborn!"
To be able to positively impact a disciple, one must care for him as he would care for his own flesh and blood. And if one wishes to gain from a mentor, he must trust that his Rebbi or teacher has the best of intentions, just like a father or mother.