A principle is a guidline, a broad sense of direction. A pledge is how you intend to navigate in that direction. So a clarification on what the principles are is important, as it defines what labour means. It's also very, very hard for the Tories to attack it.A principle is much more woolly than a pledge.
But, when we get closer to the next election it needs to be formailsed as policies otherwise it's meaningless, despite me 100% agreeing with those principles.