Rashi quotes the medrash that this was a great תוכחה. What exactly was the תוכחה? Last year I posted the Beis Halevi's very relevant pshat ( What was Yosef asking?").
This week I heard a different pshat in the name of the Chofetz Chaim. He explained that the simple fact that Yosef revealed himself was the Tochacha. As soon as the brothers saw Yosef as the King they realized without Yosef saying or doing anything that their whole outlook had been wrong and mistaken. The same thing applies to us when we go up to heaven. The simple fact that we see that Hashem really exists will be the greatest Tochacha. The only way a person can do an aveira is to deny the existence of Hashem on some level. If they really felt Hashem's presence there would be no way to do an aveira. Therefore the simple act of revealing himself will be the tochacha.