“If the rav is similar to an angel of the Lord, let them seek Torah from his mouth.” An “angel” means he has no evil inclination, as our sages said, “When Moses rose to heaven, the angels said, ‘Place your glory over the heaven.’ The Creator said [to Moses], ‘Give them a convincing answer.’ He [Moses] said to them, ‘Do you have evil inclination?’” (Shabbat [Sabbath] 88b). That is, an angel has no evil inclination.
For this reason, we should interpret “If the rav,” meaning that the rav says that each one will be similar to an angel, meaning that the disciples will have equivalence of form like an angel, who has no evil inclination, they should seek Torah from his mouth.
That is, they should seek Torah from the rav concerning how to achieve equivalence with an angel, since it is impossible to subdue the evil unless through the Torah, as our sages said, “I have created the evil inclination; I have created the Torah as a spice.”
And if not, meaning if the rav does not teach them how to be like an angel, “let them not seek Torah from his mouth,” since his Torah is not going in the true direction.