Answer: All of the above.
Although uncommon in the past, modern theatre has warmed up towards the idea of including the audience in the performance. This is an example of this practice. By having the bride and groom enter the stage through the audience, Wilder is able to bring the action even closer to the audience, and in this way immerse them even more into the story. It also breaks down traditional barriers between performers and audience. Finally, by bringing the actors so close to the audience, the act enhances the concept of universality.