Essentially this is referring to the fact that the “principles” of Dhamma, such as impermanence, dependent origination, or the four noble truths, are laws of nature and do not change.
That doesn’t mean that they are permanent, of course, because they are not “things”. They are, rather, “descriptions inferred from experience” (upādāya paññatti). Right now we can describe our experience as impermanent. A minute ago we could describe it as impermanent. A year ago, or indeed, at the start of the Universe, we could describe it as impermanent, and we would be correct. In the future, too, these principles remain the same.
It is because these “principles” always accurately describe nature that they have a liberative power. We are not just being freed from whatever this is right now, but from all things in the past and future. Even though we don’t experience them directly, we infer their nature by understanding the “stability of natural principles”.