What is gained by having Tartuffe appear for the first time in the third act?

Basically the character of Tartauffe has been built up for two acts. We heard about Tartuffe from all sorts of people yet he has never actually appeared in the story. When he does arrive, we see that he lives up to the things that have been said about him. The reader wonders if he is as hypocritical as he has been made out to be. When Tartauffe boldly commands that his "hair shirt" be "hung up", we feel as if we know this guy already.