וַאֲנִ֥י אַקְשֶׁ֖ה אֶת־לֵ֣ב פַּרְעֹ֑ה וְהִרְבֵּיתִ֧י אֶת־אֹתֹתַ֛י וְאֶת־מוֹפְתַ֖י בְּאֶ֥רֶץ מִצְרָֽיִם׃
And I will harden Pharaoh’s heart, and multiply My signs and My wonders in the land of Egypt.
Read Kabbalistic (mystical) interpretations of Exodus 7:3: Zohar and classical Jewish mystical sources, free online.