We find ourselves in the time period of the three weeks in which the Beis Hamikdash was destroyed, primarily due to the sin of baseless hatred, sina'as chinam. Therefore, in rectification, ahavas chinam is something that should be focused on and worked upon during these days.
The Mishna says (Avos 1:12), “Be from among the students of Aharon, love peace, and run after peace.” The Zera Shimshon asks: Why does the Mishna have to preface that one should be from the students of Aharon? If the Mishna is trying to teach one to pursue peace, this introduction appears to be unnecessary. The lesson is clearly expressed without it.
The Zera Shimshon explains that this introduction is actually a very important indicator of how one should pursue peace. When pursuing peace, it is possible to make the following mistake. The Gemara says (Pesachim 113b) that someone who sees his friend sin is allowed to hate him. One would think that, this being the case, there is no peace with sinners, and they would not have been included in a simple statement said by the Mishna that one should pursue peace. The fact that the Mishna makes the introduction that one should be from among the students of Aharon is actually a teaching of how one should pursue peace with sinners.
Aharon's method was to show a very friendly face to sinners. This would cause them to have remorseful thoughts. They would think to themselves, “If Aharon would only know what a sinner I was, he would not be so friendly towards me.” This would cause them to repent. By being on good terms with everyone, Aharon caused even sinners to come closer to Hashem. This is why the Mishna prefaces the statement that one should pursue peace with the statement that one should be from the students of Aharon, to teach how peace should be made with the wicked in order to bring them back and not totally alienate them.
Elsewhere, in a lesson along similar lines, the Zera Shimshon explains another Mishna.
The Mishna says (Avos 4:20), הוי מקדים בשלום כל אדם, always be the first one to greet others. A seemingly contradictory statement is taught by the Zohar (1:171b) that one may not greet sinners unless they greeted him first.
The Zera Shimshon explains that this does not mean that one may not be the first one to greet sinners; rather, the wording of the Zohar is very specific. It says that one may not greet the wicked with שלום. This does not mean that one may not greet them before they've greeted him. It means that since they are wicked, one may not use the word shalom to greet them, since Shalom is the name of Hashem. When the aforementioned Mishna says that one should be the first to greet others, it says one should ask בשלום, regarding the welfare, of others. Therefore, it does not contradict the teaching of the Zohar, since it doesn't mean that one should greet everyone using the word shalom. Rather, it means that one should inquire about their welfare.
