וַיַּ֣רְא אַהֲרֹ֔ן וַיִּ֥בֶן מִזְבֵּ֖חַ לְפָנָ֑יו וַיִּקְרָ֤א אַֽהֲרֹן֙ וַיֹּאמַ֔ר חַ֥ג לַיהוָ֖ה מָחָֽר׃
And when Aaron saw this, he built an altar before it; and Aaron made proclamation, and said: ‘To-morrow shall be a feast to the LORD.’
Read Jewish philosophical commentary on Exodus 32:5: and classical philosophical sources.