Why history is a lot more interesting than I thought

I read something new at Faith and Theology here . Since Dr. Myers and Archbishop Rowan Williams and the famous historian Quentin Skinner all say this, there probably is something true in it. What they say is that we should not judge history from today's perspective. Like separating bran from wheat. This is because doing so would mean that we claim to have the ultimate clarity in knowing things - which certainly isn't true. So what we can gain from history is to try and see how it was that people at that time could hold something we absolutely hate or absolutely take for granted as true today.

Only by sympathetically getting into the "epistemic rationality" of that day can we learn from history.

Judge ye not

from the wise Dr. Ben Myers here (talking about a method of learning from the thoughts of great men of the past ):

.. If we learn from the past by distinguishing the timeless “perennial core” from the nonessential (i.e. flawed) elements, then we’re acting as though our own commitments are the final arbiter of history — we’re assuming that history has found its goal in us. And one of the unfortunate side-effects of this approach is that we’re no longer in a position to be critiqued by history. ...

The thing I can't understand is the side effect thing. May be what we choose to understand as the perennial elements are not correct and thus open us to critique ?