Throughout Parshat Noach, man is offered many opportunities to save the world from the impending destruction. However, the people who lived during the time of the flood continued to act immorally. Finally, God's mercy reached its limit.
However, there was Noach. Noach was the savior of all of mankind because of his righteousness. Noach teaches us that one should never think of himself as insignificant and thereby unable to make a difference in the world.
One would have expected the survivors of the flood and their immediate descendants to have learned their lesson and act in a moral and proper manner. However, within a few generations, people were involved in waging a war against Hashem. At the time of Migdal Bavel, eyewitnesses of man's foolishness and its consequences where still alive. For these people, history repeated itself. Man refused to learn the lesson that God was trying to teach.
We must strive to achieve a level where we can learn from our past mistakes, thereby preventing the repetition of those very same errors.