Inside are two very ornate knives. One for him, the other for her. They are clearly more ceremonial than practical, and also clearly a matching set. Inside is a note, say roughly the following.
Congratulations on your marriage! Inside, as you no doubt are aware, are too knives. These knives, however, serve as a sort of Permenant scrying effect between each other. Spells can be cast through the knife, as well as it granting you the ability to see in the dark.
The knives can scry over nearly any obstacle, including inter-planar distances.
Again, congratulations!
HHHHHHHHHHYours Truly,
HHHHHHHHHHHHHHHHHHHHShas'aia Toriia, Overseer (leader) of AMEN, plus other titles.