כִּי֩ יְדַבֵּ֨ר אֲלֵכֶ֤ם פַּרְעֹה֙ לֵאמֹ֔ר תְּנ֥וּ לָכֶ֖ם מוֹפֵ֑ת וְאָמַרְתָּ֣ אֶֽל־אַהֲרֹ֗ן קַ֧ח אֶֽת־מַטְּךָ֛ וְהַשְׁלֵ֥ךְ לִפְנֵֽי־פַרְעֹ֖ה יְהִ֥י לְתַנִּֽין׃
’When Pharaoh shall speak unto you, saying: Show a wonder for you; then thou shalt say unto Aaron: Take thy rod, and cast it down before Pharaoh, that it become a serpent.’
Read kabbalistic (mystical) interpretation of Exodus 7:9: and classical mystical sources.