Most gatherings announce themselves as administration: a calendar hold, a form, an agenda. The evening then has to climb out of that first impression.
Anticipation is part of the experience
A sealed envelope does something a link cannot: it has weight, it takes two hands, it asks to be opened. From that moment the guest is already inside the story, days before the doors do their part.
Design the invitation with the same care as the finale. It is the only part of the night a guest can hold beforehand, and the first proof of how much the relationship matters.