“And he who [continually] declares [others] unclean is [himself] unclean and never speaks in praise [of people]. And Shemu’el said: With his own blemish he stigmatizes [others] as unclean” (BT Qiddushin 70a).
“It has been taught: The people of Israel are called holiness, and since they are holiness, one is forbidden to call his fellow a shameful name or to invent a nickname for him. The punishment for this is severe, all the more for other words. It has been taught: It is written, Keep your tongue from evil… [and your lips from speaking deceit] (Psalms 34:14). What does מֵרָע (me-ra), from evil, mean? That because of evil speech, מַרְעִין (mar’in), disease, descends to the world. Rabbi Yose said, ‘Whoever calls his fellow something he is not, or insults him, will be punished for something he did not do. For Rabbi Ḥiyya said in the name of Rabbi Ḥizkiyah, ‘Whoever calls his fellow wicked is cast down into Hell and struck on his jaws—except for those who are impudent toward Torah, whom one is permitted to call wicked.’
A certain man cursed his fellow. Rabbi Yeisa passed by and said to him, ‘You have acted like the wicked!’ [The man] brought him before Rabbi Yehudah. [Rabbi Yeisa] said to him, ‘I didn’t say ‘wicked,’ but ‘like the wicked,’ exhibiting behavior like the wicked; but I didn’t say that he was wicked! Rabbi Yehudah came and put the case before Rabbi El’azar, who said, ‘Surely, he is not guilty! How do we know? As is written: YHWH was like an enemy (Lamentations 2:5)—like an enemy, and not an enemy. For otherwise, not a stump of Israel would have remained in the world. Similarly, She has become like a widow (ibid. 1:1)—and not a widow; like a widow, [like a woman] whose husband has journeyed across the ocean and she waits for him. Rabbi Ḥiyya said, ‘From here it is proven—the essence of all—as is written: upon the image of the throne, an image like the appearance of a human (Ezekiel 1:26)—like the appearance of a human, and not the appearance of a human.’ Rabbi Yitsḥak said, ‘It is written: Like an apple tree among the trees of the forest, so is my beloved among the young men (Song of Songs 2:3)—like an apple, and not an apple; like an apple, variegated in its colors, and in colors unified.’ Rabbi Yehudah said, ‘If I have come here just to hear these words, it is enough for me!” (Zohar 2:122a, cf. ibid. 3:84b-85b).