יְלָדִ֣ים אֲשֶׁ֣ר אֵֽין־בָּהֶ֣ם כָּל־מאום [מוּם֩] וְטוֹבֵ֨י מַרְאֶ֜ה וּמַשְׂכִּילִ֣ים בְּכָל־חָכְמָ֗ה וְיֹ֤דְעֵי דַ֙עַת֙ וּמְבִינֵ֣י מַדָּ֔ע וַאֲשֶׁר֙ כֹּ֣חַ בָּהֶ֔ם לַעֲמֹ֖ד בְּהֵיכַ֣ל הַמֶּ֑לֶךְ וּֽלֲלַמְּדָ֥ם סֵ֖פֶר וּלְשׁ֥וֹן כַּשְׂדִּֽים׃
youths in whom was no blemish, but fair to look on, and skilful in all wisdom, and skilful in knowledge, and discerning in thought, and such as had ability to stand in the king’s palace; and that he should teach them the learning and the tongue of the Chaldeans.
Sichot HaRan
And he also does him a favor, when the Tzadik needs to go from level to level, then they try him, whether he has power to stand in the hall of the King (Daniel 1:4). And the hall of the King is the aspect of the mouth of the Tzadik which is called heikhal which is gematria Ad-nai which is the aspect of mouth, as is written, "malkhut -- peh/Kingship [is] the mouth."