Inviting us into their world:
The wording of the invitation says, quote, "request the pleasure of your comapny." Such wording, typical on such invites, suggests that the viewer is not merely invited to be in the audience of the wedding, but that the viewer is desired to interact with the main characters and the other guests
Scully's body language in the picture also suggests an open invitation to join their world.
-Her direct gaze is as if she can really see you.
-This effect is strengthened by the shadows around her eyes, which direct her towards you at most angles
-The location of her hand, as if she had just patted it against
her upper leg in a "come here" gesture