Chastity, her first duty and ideal, is nothing less than a Cause to which she is sworn; she must not desert it despite the world. Therefore, that which a maiden is, and which she has always persisted in being, is her self in the truest sense of the word, for it is the very stuff of her conscious existence. It is what she is in the world. And so Diana, as she put forth her hand to accept the ring from such a man as Bertram (who was already married to another) felt that she was truly forsaking herself. She would no more be the girl she was.
It is probably unnecessary to dwell further upon this point of view—Shakespeare's expression of it is sufficient. The circumstances being understood and the meaning of this word fixed, it now devolves upon us to explain, if possible, the figure of speech by which Shakespeare wished to make it all more forceful and vivid. And as to what a "scar" is, or scaur (formerly spelled scarre) there ought to be no great doubt about that, especially in the light of the context.
"Scar—A bare and broken place on the side of a mountain, or in the high bank of a river; a precipitous bank of earth."—Webster's Dictionary (1890).
We are all supposed to understand Tennyson easily enough when he writes:
O, sweet and far, from cliff and scar,
The horns of elfland faintly blowing.
In Shakespeare's day we find it spelled "scarre," and so his conception of the word