Each glorifies the Triumph of the Incarnate Word, with this difference: that on the south porch Our Lord is not exalted alone as He is on the west front, but in the person also of the Elect and of His Saints.

If to these two subjects, which may be considered as one--the Saviour glorified in Himself and in His Saints--we add the praises of the Virgin set forth in the north front we find this result: a poem in praise of the Mother and the Son as declaring the final cause of the Church itself.
"By studying the variations between the south and west fronts we perceive that, though in both Jesus is shown in the same act of blessing the earth, and though both are almost exclusively restricted to illustrating the Gospel, leaving the scenes of the Old Testament to the arches on the north, they differ greatly from each other, and are no less unlike the portals of all other cathedrals.
"In total disagreement with the mystic rituals observed almost everywhere else--at Notre Dame de Paris, at Bourges, at Amiens, to name but three churches--the Last Judgment, which is seen on the main entrance of those basilicas, is at Chartres relegated to the south porch.
"And in the same way the Tree of Jesse, which at Amiens and Reims and the cathedral at Rouen, is displayed on the royal porch, is at Chartres on the north side of the building; and many more similar changes might be noted," said Durtal to himself.

"But, which is yet more strange, the parallel so commonly to be observed between the subjects treated on the inner and outer surface of the same wall, in sculptured stone without and painted glass within, does not constantly exist at Chartres.

This, for instance, is the case with regard to the genealogical Tree of Christ, which is seen inside in glass on the upper wall of the west front, and is carved outside on the north porch.

At the same time, when the subjects do not entirely coincide on the front and back of the page, they are often complementary, or carry out the same idea.