Halakhah sa Malakias 2:7: Mishneh Torah, Torah Study & Sefer HaChinukh

No instructions in the Torah should be given to any but a fit student of proper conduct, or to one indifferently known; but if one followed a way which is not good, we first must bring him back to goodness and lead him in the path of righteousness and scrutinize him, after which we may admit him to the Beth Hamedrash and give him instructions. The sages said: "He who instructs an unfit disciple is likened unto one who serves Mercury by casting a stone upon him, as it is said: "As a small stone in a heap of stones, so is he that giveth honor to a fool'" (Prov. 26.8; Hullin, 133a). There is no honor save in the Torah as it is said: "The wise shall inherit honor" (Prov. 3.35). Likewise, a Rabbi who does not follow the good way, though he be a great scholar and all of the people stand in need of him no instruction should be received from him until his return to goodness, as it is said: "For the priests' lips should keep knowledge and they should seek the Law at his mouth; for he is the messenger of the Lord of Hosts" (Mal. 2.7). Thereupon the sages said: "If the Rabbi be like unto the messenger of the Lord of Hosts then shall they seek the Law at his mouth, if not, they shall not seek the Law at his mouth."¹Ta’anit, 7b; Mo’ed Katan, 16a; Makkot, 10b. C. G.

And [it] is practiced in every place and at all times by males and females. Anyone who transgresses it and consecrates an [animal] with a blemish — and even at this time — violates this negative commandment. And from what appears, there would not be lashes with this, since there is no act [involved] with it; but I saw that Rambam, may his memory be blessed, wrote (Mishneh Torah, Laws of Things Forbidden on the Altar 1:2) [that] one who consecrates an [animal] with a blemish is lashed. And maybe he makes it like one who exchanges [a sacrifice] about which there is lashes even though there is no act [involved] with it — as [in that case, we see the impact of his words — since] this and that are consecrated. And to him shall we listen “and we will seek Torah from his mouth, as he is an angel of the Lord of hosts.”