organisation routes rails -- restful_authentication, event /login

i am struggling lane setup rails application. i have hallowed restful_authentication mostly followed instructions. i have set adult routes way:

map.login '/login', :controller => 'sessions', :action => 'new'
map.logout '/logout', :controller => 'sessions', :action => 'destroy'
map.resource :session

if you're logged in, you're redirected .
it creates kind sense, formula lib/authenticated_system.rb says redirect_to new_session_path.

but i guess routes mapping ostensible work both ways (code url url code). someone explain? thanks