וַיֹּ֤אמֶר מֹשֶׁה֙ אֶֽל־אַהֲרֹ֔ן מֶֽה־עָשָׂ֥ה לְךָ֖ הָעָ֣ם הַזֶּ֑ה כִּֽי־הֵבֵ֥אתָ עָלָ֖יו חֲטָאָ֥ה גְדֹלָֽה׃
And Moses said unto Aaron: ‘What did this people unto thee, that thou hast brought a great sin upon them?’
Read kabbalistic (mystical) interpretation of Exodus 32:21: and classical mystical sources.