Sin is Ethical not Metaphysical

I first heard this phrase used by an open theist that I am acquainted with (Jesse Morrell). I did not understand what he meant by it.

This is interesting to note since this phrase, I believe, was coined by Cornelius Van Til, a premier Calvinist philosopher and theologian and Professor of Apologetics at Princeton Theological Seminary then Westminster Theological Seminary.

As I was listening to an Apologetics course taught by John Frame (you can download it for free) I heard him use this phrase/similar phrase(?). I looked it up online and found that Frame cites Van Til.

On another site I found that Frame attributed this phrase as a paraphrase of Herman Bavinck ("...the source is Bavinck..."), another Calvinist theologian/philosopher. I believe that I have discovered the volume in which Bavinck expounds this; his Reformed Dogmatics: Volume 3 Sin and Salvation in Christ.

Update: Bavinck is difficult to read but well worth the money spent and I've barely put a dent in the book.