Verse 15 already said that Hashem cleaved rocks and gave water. Why is this repeated?
Radak: The matter is repeated in different words to strengthen it, like is common.
Malbim: Do not say that there was a spring here. He took water out from the rock, from the well of Miryam.
Why does it say "va'Yored ka'Neharos Mayim"?
Rashi: Water flowed from the well [of Miryam]. Each Nasi dug a furrow with his staff, and the water went to the encampment of his Shevet - "bi'Mchokek b'Mish'anosam" (Bamidbar 21:18).
Radak: The rock [from which the water came] was tall, therefore it says "va'Yored".
Malbim: Even though the water was from a lone rock that traveled with them in the Midbar from place to place, "He brought water like rivers."
