Kommentar zu Schemot 10:27

ויחזק ה׳ ..ולא אבה, G'd hardened Pharaoh's heart and he did not want to dismiss, etc. The Torah testifies that on this occasion Pharaoh decided not to let the Israelites go, period. He no longer weighed the pros and cons but decided to hang tough even if this should cost him his life. This is why the Torah attributes this decision to him with the words לא אבה.

V. 27.ויחזק : durch die immer mehr schwindende Finsternis.

Alternatively, he tried to outsmart G'd and Moses by analysing the pattern of the plagues to-date. There had always been two plagues which he was warned about followed by a plague without warning. The last plague, darkness, had not been preceded by a warning. Pharaoh realised that if there were to be another plague, G'd would first warn him. By denying Moses access to the palace he hoped to prevent Moses from issuing the warning which he thought had to precede the next plague. Since Moses was aware that there was only one plague to follow and that G'd would not need to harden the heart of Pharaoh again in order to have an excuse to inflict further plagues upon him, he was able to respond immediately: כן דברת לא אוסיף עוד ראות פניך, "you are quite right; I am not going to see you again, ever." I have already commented on Moses' response in connection with Exodus 7,3 ואני אקשה.