The word Then is only transitional and does not indicate how soon this plague followed the previous one. Some translators may wish to connect this chapter more clearly to the previous one; for example, “After the great hailstorm had ended, the LORD said to Moses.” Go in to Pharaoh may suggest that Moses is to meet the king inside the palace, even though most translations do not reflect this. The Hebrew word means “to enter,” but it can also mean “Go into Pharaoh’s presence” (New English Bible). (See the comment at 8.1.)

For I have hardened his heart is literally “because I, I hardened his heart.” The conjunction for is causal and the pronoun I is emphatic. This clearly shows that Yahweh actually intended to make the king “stubborn” before sending Moses to him again. Therefore I have hardened his heart, or “I have made him … stubborn” (Good News Translation), should be shown in contrast to the idea in 9.34-35 that the Pharaoh hardened his own heart. The word for hardened here has the basic meaning of heavy or dull. (See the discussion at 4.21 and 7.13.) And the heart of his servants may need to be pluralized, as in New International Version (“the hearts of his officials”).

That I may show should be understood as “in order that” (Good News Translation), for it explains why the LORD hardened his heart and introduces the first of two stated purposes of the plagues—that I may show. (The second purpose is stated in verse 2.) These signs includes all the “miracles” performed in the negotiations with the Pharaoh, not just the seven disastrous plagues that have already occurred. Signs of mine clearly shows that Yahweh is the one performing them. Hence Good News Translation, “in order that I may perform these miracles.” (For signs and “miracles” see 3.20.) Among them in the Hebrew is literally “before him” (King James Version), but it refers to the king and his officials. (Hebrew Old Testament Text Project states “The singular is collective.”) One may also express among them as “in their sight” or “as the king and his officials are watching.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .