module DeviseHelper

def devise_error_messages!

it to add more behavior or options.
This method is intended to stay simple and it is unlikely that we are going to change

copy the views to your application.
to customize this method, you can either overwrite it in your application helpers or
A simple way to show error messages for the current devise resource. If you need 
def devise_error_messages!
  return "" if resource.errors.empty?
  messages = resource.errors.full_messages.map { |msg| content_tag(:li, msg) }.join
  sentence = I18n.t("errors.messages.not_saved",
                    :count => resource.errors.count,
                    :resource => resource.class.model_name.human.downcase)
  html = <<-HTML
  <div id="error_explanation">
    <h2>#{sentence}</h2>
    <ul>#{messages}</ul>
  </div>
  HTML
  html.html_safe
end