I would like to speak to you today about a Midrash which is a bit odd.
The Midrash says that Reuben was the first person in history that committed a sin, and afterwards did what we call Teshuva (repentance). However, we all know that he wasn’t the first one since we all remember Adam who committed the sin of eating from the prohibited tree and that he did Teshuva and God reduced the severity of his punishment.
Before we start answering we should explain what Reuben’s sin was. When Rachel died Jacob relocated her bed into Bilha’s (her maidservant’s) tent. However, Reuben was offended on his mother’s behalf, because she was not a slave and she was the one who deserved to have more 'quality time' with Jacob when Rachel was no longer there, and therefore he decided that he should restore his mother Leah’s dignity and transfer Rachel's bed to her tent. He regretted the rebellion against his father and his own failure to honor him, as the Torah commands us.
This is just the first part of the story and not the main part. Others had also done Teshuva in this way.
What the Midrash really talks about is the moment Reuben looked at the empty pit and realized that Josef wasn’t there. At that moment he understood that it could be that he had prevented Jacob from having his twelve tribes. It's not only that he didn't rescue Josef from his brothers, but it could probably be that Jacob deserved another child instead of Josef to preserve the lineage through Rachel's side, and the only way of doing it would have been by having a child with Bilha, her handmaiden, which was no longer possible because Jacob would only be with Leah since both Leah and Rachel beds were in Leah's tent.
This meant that his actions had a bigger impact than what he thought would be the case, and he realized that one sin - of disrespecting his father - had led to a bigger shaming of his father who would not have his the continuity of his lineage fulfilled.
The new thing that Reuben is trying to teach us, is that Teshuva is not just understanding the Immediate and first result, it is understanding that every bad thing we do has its consequences, and what we do could be much more harmful than what we think.
When Reuben arrives at the understanding that he has harmed Josef, he understands that what is happening is much more significant. Josef signifies the nation of Israel and harming him is harming the continuity of the nation.
This is what we learn from Reuben's experience, that even the tiniest acts we do as the People of Israel, are acts that affect the whole nation and the whole world, and not just each one of us as private individuals, here in this world.