(א) וַיֹּ֤אמֶר ה' אֶל־מֹשֶׁ֔ה רְאֵ֛ה נְתַתִּ֥יךָ אֱלֹקִ֖ים לְפַרְעֹ֑ה וְאַהֲרֹ֥ן אָחִ֖יךָ יִהְיֶ֥ה נְבִיאֶֽךָ׃ (ב) אַתָּ֣ה תְדַבֵּ֔ר אֵ֖ת כׇּל־אֲשֶׁ֣ר אֲצַוֶּ֑ךָּ וְאַהֲרֹ֤ן אָחִ֙יךָ֙ יְדַבֵּ֣ר אֶל־פַּרְעֹ֔ה וְשִׁלַּ֥ח אֶת־בְּנֵֽי־יִשְׂרָאֵ֖ל מֵאַרְצֽוֹ׃ (ג) וַאֲנִ֥י אַקְשֶׁ֖ה אֶת־לֵ֣ב פַּרְעֹ֑ה וְהִרְבֵּיתִ֧י אֶת־אֹתֹתַ֛י וְאֶת־מוֹפְתַ֖י בְּאֶ֥רֶץ מִצְרָֽיִם׃ (ד) וְלֹֽא־יִשְׁמַ֤ע אֲלֵכֶם֙ פַּרְעֹ֔ה וְנָתַתִּ֥י אֶת־יָדִ֖י בְּמִצְרָ֑יִם וְהוֹצֵאתִ֨י אֶת־צִבְאֹתַ֜י אֶת־עַמִּ֤י בְנֵֽי־יִשְׂרָאֵל֙ מֵאֶ֣רֶץ מִצְרַ֔יִם בִּשְׁפָטִ֖ים גְּדֹלִֽים׃ (ה) וְיָדְע֤וּ מִצְרַ֙יִם֙ כִּֽי־אֲנִ֣י ה' בִּנְטֹתִ֥י אֶת־יָדִ֖י עַל־מִצְרָ֑יִם וְהוֹצֵאתִ֥י אֶת־בְּנֵֽי־יִשְׂרָאֵ֖ל מִתּוֹכָֽם׃
(יג) וַיֶּחֱזַק֙ לֵ֣ב פַּרְעֹ֔ה וְלֹ֥א שָׁמַ֖ע אֲלֵהֶ֑ם כַּאֲשֶׁ֖ר דִּבֶּ֥ר ה'׃ {ס}
(יד) וַיֹּ֤אמֶר ה' אֶל־מֹשֶׁ֔ה כָּבֵ֖ד לֵ֣ב פַּרְעֹ֑ה מֵאֵ֖ן לְשַׁלַּ֥ח הָעָֽם׃
We find three nuances of קשה:
אקשה, אכבד, אחזק.
אַקְשֶׁ֖ה: to be hard in general, not to absorb an impression, letting everything pass without an impression.
וַיֶּחֱזַק֙: solid, but works against its consciousness. Even the impression gets totally lost.
כָּבֵ֖ד: difficult, something can receive an impression, but there is still a wide gap between the impression and the moment of letting oneself be guided by this impression: difficult to bring into motion. However, this moment can be achieved, albeit with effort.
Pharaoh's initial insensitivity becomes a means of laying down a treasure of אותות and מופתים in Mizrajim, from which all subsequent times can draw the knowledge and conviction of God's omnipotence, presence and administration in history. From now on, no more נסים need to happen, because they have already happened there.
From this we can learn that even when we don't understand the reason for something we can be sure that 'ה has a plan with it for us.