What is the subjuct of the very fist line of the play? Why does it begins with this topic?

Now, fair Hippolyta, our nuptial hour

Draws on apace. Four happy days bring in

Another moon. But oh, methinks how slow

This old moon wanes! She lingers my desires,

Like to a stepdame or a dowager

Long withering out a young man’s revenue.

The subject is an impatient bridegroom waiting for his wedding day......... this is what it's all about. Young impatient love and more than one couple.