What will Mitzrayim hear?
Rashi: They will hear that Hashem will have massacred the whole of Yisrael.
What exactly will they then say? How does "Vesham'u ... ki He'elisa be'Chochacha ... " fit into the picture?
Rashi and Seforno: Having seen how Hashem took Yisrael out of Egypt with great strength, they will therefore draw the conclusion that, although He was able to defeat them, he subsequently killed Yisrael - not because they sinned to him, but - because He was not capable of defeating the Cana'anim. 1
Rashi and Seforno: In fact, this theme repeats itself in the following three Pesukim in a more detailed fashion, as we will now explain.