The French people are angry and upset about the recent terrorist attack. The affect has been much like the attack at Pearl Harbor was for the United States in WWII. Persians are starting to take this war much more serious and they will be more sympathetic to the soldiers who are fighting.
The Nice, France attack will make the French take the fight against ISIS more seriously because they have now been the subject of two attacks, and the frequency of these attacks in other countries is not slowing down. The French government now knows they must step up their anti-ISIS fighting simply to protect their own citizens as it is a proven problem.
I am not saying that France has not taken the fight against ISIS seriously all along however I do feel when a country is personally attacked, it more or less hits its citizens deep in the gut. Once it feels like a personal attack the seriousness of the fight has to grow.
The terrorist attack in Nice is still not likely to make the French government take defeating ISIS seriously. France has yet to commit the military resources necessary to win a war against ISIS. Furthermore, France does not provide NATO with a lot of support when it comes to fighting terrorism. Therefore, even after the latest terrorist attack in France, it is unlikely that the government will be swayed to take the fight against ISIS more seriously.