אֶת־מִי֙ יוֹרֶ֣ה דֵעָ֔ה וְאֶת־מִ֖י יָבִ֣ין שְׁמוּעָ֑ה גְּמוּלֵי֙ מֵֽחָלָ֔ב עַתִּיקֵ֖י מִשָּׁדָֽיִם׃
Whom shall one teach knowledge? And whom shall one make to understand the message? Them that are weaned from the milk, Them that are drawn from the breasts?
Read kabbalistic (mystical) interpretation of Isaiah 28:9: and classical mystical sources.