tn The verb is רִיב (riv); it is often used in the Bible for a legal complaint, a law suit, at least in form. But it can also describe a quarrel, or strife, like that between Abram’s men and Lot’s men in Genesis 13. It will be the main verb behind the commemorative name Meribah, the place where the people strove with God. It is a far more serious thing than grumbling—it is directed, intentional, and well-argued. For further discussion, see J. Limburg, “The Root ‘rib’ and the Prophetic Lawsuit Speeches,” JBL 88 (1969): 291–304.
tn The particle לוּ (lu) indicates the optative nuance of the line—the wishing or longing for death. It is certainly an absurdity to want to have died, but God took them at their word and they died in the wilderness.