אור החיים — והיו המים אשר תקח מן היאר

Q — In the third sign given to Moshe, why does the verse double the word 'והיו' — 'the waters you take from the Nile והיו לדם ביבשה'? Rashi says it teaches the water turned to blood only upon reaching dry land, not in Moshe's hand — but why should that detail matter?

A — Or HaChaim adds a reason: Chazal teach that Moshe could not strike the Nile, because it had protected him as an infant (which is why Aharon struck it during the plague). Here too, God arranged that the miracle should not occur through Moshe's agency. Hence 'והיו' — the water stays in its natural state the whole time it is in Moshe's hand, and only becomes blood once it reaches the ground. The doubling preserves Moshe's debt of gratitude to the river.