1)
Why must they thank Hashem?
1.
Malbim: (a) For the Chesed that He did with them. (b) For the miracle. Even though it is not wondrous for Hashem, for people it is wondrous.
2)
Why does the verse teach about "Nifle'osav"?
1.
Radak: When they reach a settled city, they tell people the wonders that Hashem did for them.
