In "chocolat" how Vianne change Lansquenet's people ideologies through chocolate? What is the battle for?
The people of Lansquenet-sous-Tannes are guilted into abstaining from chocolate because it is Lent, a time when people are supposed to abstain from earthly pleasures as a way of atoning for sin and entering into the suffering of Christ. Lent is the 40 days leading up to Easter Sunday and many Catholics give things up during this time to honor Christ. Vianne's chocolate, however, is magic, and the people are tempted to eat it anyway because it is so delicious. Plus, she instinctively knows which kind is everyone's favorite.
The parish priest wants to have Vianne run out of town because she is an evil temptress with her chocolate, but she believes that life is hard enough and people should be able to indulge in a little pleasure. The people of the village sneak into the choclate shop for just a little taste in spite of the priest's warnings. Vianne prepares a huge chocolate festival for Easter Sunday because on Easter Sunday, Lent will be over. This is ironic because Easter is also the day on which Christ rose from the dead, freeing people from sin. Christ has done the work of redemption, not humans, so giving things up for Lent is merely a human work and the Bible teaches that works do not get people into heaven. God's grace and forgiveness gets people into heaven through Christ's atoning work on the cross. So in a way, Vianne is more right-on with God's purpose than the religious priest.
I think the battle is over people's beliefs. The priest wants the people to believe like he does and live an ascetic life, but Vianne lives an abundant life of joy and wants to share her joy with everyone.