If you want Devise to do validations, you need to add the :validatable module to your model. This is fairly easy to do, just add :validatable to the list of module in the devise call, so your model says:
devise
:database_authenticatable,
:lockable,
:registerable,
:recoverable,
:rememberable,
:trackable,
:validatable
This will make devise add validations.
Another easy way is to add your own validations. If you just want to validate that the password confirmation matches, you can add a validates_confirmation_of validation by adding this to your model:
validates_confirmation_of :password
I hope this helps.