How to return invalid form fields back to the page?

It's a classic case of create and edit a form data. I got a complex form that suppose to render back all fields to validate it, but doesn't works. For this case, I've created a simple example to illustrate my concern and try to understand what's happing.

In this sample app body parser and method override are up:

app.use(express.bodyParser());
app.use(express.methodOverride());

Now I have a simple form in user.jade:

doctype 5
html
    header
        title Add new user
    body
        h4 User - Add
        form(id='userForm', method='post', action='/user/save')
            label(for='name') Name
            input(type='text', id='name', name='name')
            label(for='address') Address
            input(type='text', id='address', name='address')
            input(type='submit', value='Save')

The GET and POST HTTP Methods are configured:

app.get('/user/new', user.create); //create new user
app.post('/user/save', user.save); //save or edit user in validation process

Finally the "create" and "edit/save" functions:

exports.create = function(req, res) {
    res.render('user');
};

exports.save = function(req, res) {
    var name = req.body.name;
    var address = req.body.address;

    //do some validation
    //...

    //return it back to page to fix wrong fields
    res.render('user', { name: name, address: address });
};

Why I render user.jade back, so the fields are not filled? Can't use res.render to fill page form? Thanks in advance!