render() - how it loads controllers?

I give 401 Uanthourised acces header with

module.exports = function() {

    return function(req, res, next) {

        if (!req.isAuthenticated()) {
            res.status(401);
            console.log('Unauthorized');

            res.render('login.html', { csrfToken: req.csrfToken() });

            return;
        }

        next();
    };
};

Now login.html is a view handled by completly different controller:

var passport = require('passport');
var config = require(__dirname + '/../lib/config');

module.exports = function (router) {

    router.get('/', function (req, res) {
        // Error flash messages
        var errorFlash = req.flash('error');
        if (errorFlash && errorFlash.length) {
            res.locals.error = errorFlash;
        }
        res.render('login.html', { csrfToken: req.csrfToken() });
    });

    router.post('/',
        passport.authenticate('local', {
            failureRedirect: '/login/',
            failureFlash: true
        }),
        function(req, res) {
            res.cookie(config.cookie.name, req.user.email, { signed: true, maxAge: 1234 });
            res.redirect('/');
        }
    );

};

My concern is how I can be sure what part of login controller fires up? render('index.html') somehow hooks up to router.post() in index controller and login form is handler as usual. How that can be?