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 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 into how one should pursue peace. When pursuing peace, it is possible to make the following mistake. The Gemara says (Pesachim 113b), 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 the students of Aharon, is actually a teaching of how one should pursue peace with sinners.
Aharon's method was that he showed 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 and therefore 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 the 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.
