One of the good things that come of a true marriage is, that there is one face on which changes come without your seeing them; or rather there is one face which you can still see the same, through all the shadows which years have gathered upon it.

MacDonald suggests that a “true marriage” alters perception as much as it alters lives. Living closely with one person, you do not register their gradual aging in the way you might with friends seen only intermittently; the changes arrive too slowly to be noticed as “difference.” More deeply, love becomes a kind of moral and imaginative constancy: even as time lays “shadows” (fatigue, sorrow, age) on a beloved face, the spouse continues to perceive the enduring person beneath. The line implies that fidelity is not mere endurance but a trained vision—seeing through time’s damage to what remains essentially the same, and letting affection preserve identity against the erosions of years.