When Yosef reveals himself, he asks אני יוסף העוד אבי חי. It is a very strange question. After all Yehuda just finished telling Yosef the whole story including that his father is alive, so what exactly was Yosef's question? Did Yosef think that Yehuda suddenly got a nevua that Yaakov died? In addition, Rashi quotes the medrash that this was a great תוכחה. What exactly was the תוכחה?
The Beis Halevi explains as follows. Yosef was asking a rhetorical question. Yosef told his brothers you claim that you are so concerned about your fathers health, yet, I am Yosef is my father still alive? Meaning, he asked them if you really cared for your father how could you put him through the pain of of my disappearance. He exposed the hypocrisy of Yehuda's claim that they were concerned about their father's well being through Yehuda's own actions.
Now we can also understand why this is called a תוכחה as well. This is exactly what will happen when a person goes up to שמים after 120. Whatever excuses he gives for not doing mitzvos or doing aveiros will be shown to be hypocritical by his own actions.
In previous generations it may have been hard to imagine playing back your life after you die to see what you did wrong. However, for us this should be easy to believe. After all, we see how modern technology can record every action and play it back in color with sound. We see it happening all the time when people get caught on video or on audio doing things they shouldn't be doing and the embarrassment and damage that it does (e.g. Tiger Woods, Tropper etc.). Therefore, we should understand that everything is being recorded and will be played back at the appropriate time and there will be no excuses.