Or HaChaim on Numbers 17:17/אור החיים על במדבר י״ז:י״ז

1 דבר אל בני ישראל וקח מאתם, "speak to the children of Israel and take from them, etc." The expressions דבר plus קח suggest that we are speaking about two separate subjects. G'd said דבר, referring to the fact that 1) the Israelites were to bring one rod representing their respective tribes; 2) Moses was to accept these rods from them. Although the Torah did not spell out who was to bring these rods to Moses, the letter ו at the beginning of the words וקח alludes to this. [The problem is that the Torah did not spell out exactly what it was that Moses was to take from the children of Israel. Ed.] An additional reason for the Torah to write וקח with the extra letter ו may be that this demonstration was additional to the conversion of the 250 censers into covers for the altar which had also been described as being a memorial to what happened to Korach and associates. The people had to be given visual evidence that G'd had chosen Aaron.

2מאתם…מאת כל נשיאהם, "from them…from all their princes." The reason the Torah said both מאתם and did not content itself with writing מאת נשיאהם, is to ensure that Moses would accept these rods only from the princes and that he should not set aside 12 rods on behalf of the respective tribes. Had the Torah only written that Moses was to take these rods from the princes this would not have obligated the princes to come forward and present Moses with these rods. Moses could have acted as their representative and assigned a rod for each tribe. Alternatively, we could have thought that if the Torah had only written the words מאת נשיאהם this meant that the rods should be the property of the various princes but that Moses should take them, i.e. select them; therefore the Torah added the word מאתם to teach that the princes themselves must bring these rods to Moses. At any rate, the reason the Torah was so specific was to prevent anyone from claiming afterwards that Moses had selected a rod for them that never had a chance to blossom and that therefore the fact that Aaron's rod blossomed did not prove anything.