(Bamidbar 10:3-4) "And when they (the Cohanim) blow with (both) of them, then all the congregation shall gather unto you, to the door of the tent of meeting. And if they blow with one, there shall gather unto you the chiefs." — But we have not heard to where (the chiefs are to gather). It follows (by induction), viz. "Blowing" is written in respect to the congregation, and "blowing" is written in respect to the chiefs.
Just as the first (gathering) is at the door of the tent of meeting, so, the second. I might think that all who are (written) first in Scripture (in this instance, the congregation) are first in the act (of gathering). It is, therefore, written (Bamidbar 30:2) "And Moses spoke (first) to the heads of the tribes of the children of Israel": Since "speaking" is mentioned in the Torah unqualified (as to the order of speaking), and in one instance it is explicitly mentioned that the chiefs take precedence, so I induce that in all instances of "speaking" the chiefs take precedence.
R. Yonathan said: (The above derivation is) not needed. For it is already written (Shemot 34:31-32) "And Moses called to them, and there returned to him Aaron and all the chiefs of the congregation and Moses spoke to them. And afterwards all the children of Israel drew near, etc." Since "speaking" is mentioned in the Torah unqualified, and in one instance it is mentioned that the chiefs take precedence, so I induce that in all instances of speaking the chiefs take precedence.
What, then, is the intent of "And Moses spoke to the heads of the tribes, etc."? To teach (by juxtaposition with 30:3) that annulment of vows is effected only by experts.