What is the connection between the current episode and the well?
Rashi: When the two mountains moved bak to their original locations (Refer to 21:15:2:1**), Hashem sent the well into the valley to bring up the blood, arms and limbs of the dead men and to carry them round the camp; 1 Yisrael saw and sang Shirah.
Seforno: Refer to 21:15:2:2. From Ar, the stormy waters flowed down to the valley where the well was, to a spot that was much lower than the location of Yisrael, and when the well then accompanied them to the other side of Arnon, to the point from where the streams of the River Arnon flowed down to Mo'av, they sang Shirah on the great miracle (of the water defying the laws of nature and flowing upwards). 2
Seforno: This demonstrated the fact that the water of Miriam's well was supernatural - as was evident from the fact that it flowed from the rock at Hashem's will (which would have come about via a mere verbal command - had Moshe and Aharon not struck it. Refer also to 21:14:2:1* & 21:17:3:1.
What are the connotations of "u'mi'Sham Be'erah"?
Rashi: It means that, from there, the flowing rivers came to the well. After the mountains moved back, Hakadosh-Baruch-Hu asked 'Who will inform My children about these miracles'? And He sent the well down to collect the the blood and the limbs of the dead Cana'anim and carry them round the camp.
Ramban: Continuing from Pasuk 13, it teaches us that after they traveled from the other side of Arnon without entering it, they circumvented the town of Be'erah. 1
Kidushin, 3b: Refer to 21:14:2:6.
QUESTIONS ON RASHI
Rashi writes that from there, the flowing rivers came to the well. But they had the well from the beginning of the forty years, before they came to this area?