As the "eyes of his glory" are turned upon Jerusalem and Judah, their sins are apparent to God - the "show of their countenance doth witness against them." The idea is that the face is the mirror of the soul, and that the heart may be seen in the witness of the face. Thus we have in Genesis:
Gen. 31:5 And said unto them, I see your father's countenance, that it is not toward me as before; but the God of my father hath been with me.
Likewise in the Book of Mormon we find:
Alma 5:14 And now behold, I ask of you, my brethren of the church, have ye spiritually been born of God? Have ye received his image in your countenances? Have ye experienced this mighty change in your hearts?