Why is there a Tzeirei under the Hei in "He'avarta"?
Radak: We find like this elsewhere, e.g. "Kulo b'Chakeh He'alah" (Chabakuk 1:15).
What is the meaning of "v'Lu Ho'alnu"?
Rashi: If only we had stayed in [Ever ha'Yarden, i.e. Eretz Sichon and Og, which we already conquered].
Malbim: We would have been content [to stay in Ever ha'Yarden].
Why did Yehoshua say that it would have been better to stay in Ever ha'Yarden?
Malbim: If Hashem will not go with us, and we will be left to chance (perhaps the Emori'im will conquer us), we should have stayed. A nation goes to conquer new land only if it is sure that it will win, or its land does not suffice for it. Then it will endanger itself to get more land.