Commento su Esodo 15:24

וילנו AND THEY MURMURED — This is a Niphal form, and similarly the Targum is a Niphal form: ואתרעמו (the Ithpael form in Aramaic corresponds to the Hebrew Niphal). And such is the way in which the expression denoting murmuring (from root לון) is employed: to refer back the matter (the action of murmuring) to the person (the subject of the verb); thus one says מתלונן and מתרועם and one does not say לונן and רועם. So, too, the Frenchman says “decomplaisant se” in old French, where it turns back the matter (the action) to himself (the subject) by saying, “se”, English himself.

וילונו העם על משה, The people murmured against Moses, etc. The Torah criticises the manner in which the people provoked a quarrel. The Torah does not deny the validity of a people asking for drinkable water, i.e. the question: "what are we to drink?" They should have asked for their needs in an appropriate manner.

To revert the statement to the person: מתלונן . . . I.e., meaning: [It refers] to the complainer. But the expression לונן does not revert to the complainer as much.