6 The clause begins with the emphatic use of the pronoun and a disjunctive vav (ו) expressing the contrast “But as for me, I will harden.” They will speak, but God will harden. The imperfect tense of the verb קָשָׁה (qasha) is found only here in these “hardening passages.” The verb (here the Hiphil for “I will harden”) summarizes Pharaoh’s resistance to what God would be doing through Moses—he would stubbornly resist and refuse to submit; he would be resolved in his opposition. See R. R. Wilson, “The Hardening of Pharaoh’s Heart,” 41 (1979): 18–36.
7 The form beginning the second half of the verse is the perfect tense with vav (ו) consecutive, הִרְבֵּיתִי (hirbeti). It could be translated as a simple future in sequence after the imperfect preceding it, but the logical connection is not obvious. Since it carries the force of an imperfect due to the sequence, it may be subordinated as a temporal clause to the next clause that begins in v. 4. That maintains the flow of the argument.

In other versions

But I will harden Pharaoh’s heart, and though I multiply my signs and wonders in the land of Egypt,

But I will harden Pharaoh’s heart, and though I multiply my signs and wonders in Egypt,

But I will harden Pharaoh’s heart and multiply my signs and wonders in the land of Egypt.

But I will make Pharaoh’s heart stubborn so I can multiply my miraculous signs and wonders in the land of Egypt.

And I myself will harden the heart of Pharaoh, and I will make my signs and my wonders numerous in the land of Egypt.

And I will harden Pharaoh’s heart, and multiply my signs and my wonders in the land of Egypt.

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