They forgot all the good that was done for them. A question can be asked , why were fiery snakes sent to punish them? There must be a symbolism regarding the "fiery serpents". The Torah must be teaching us a lesson. I would like to propose the following original answer, Bezrat Hashem: The fiery serpents are symbolic of the 2 types of "gossipers" that exist. One type of gossiper will only use gossip as a means to destroy a foe or competitor.This represents a serpent that will only attack when it feels threatened. While fire will consume what it can, it is indiscriminate. This represents the gossiper that speaks evil about all, friend or foe. Although the latter type (fire) is perhaps more vicious, both are nonetheless destructive.The Torah is beaconing us to be aware of these 2 types of gossipers, and perhaps discover if we fit into any of the 2 types ourselves. Before we can cure ourselves of the ills of malicious gossip, we must be aware of its existence. This is perhaps the lesson of the "fiery serpents".

Just as fiery serpents are destructive, so to is our malicious gossip equally destructive. Do we at all realize this? Are we aware of the destruction malicious gossip can potentially cause? Are we awake , or asleep? The symbolism of the fiery serpents is a means to wake us up. Have a good Shabbos..................................................................................................