In Parshas Mishpatim (23:4), the Torah introduces the Mitzvah of Hashavas Aveida by characterizing the owner of the lost animal as “אויבך”, your enemy. Similarly, in the next Pasuk, the Mitzvah of P’rika (unloading), the owner is referred to as “שונאך”, someone you hate.
The Gemara famously explains that the “hated / enemy” must be a sinner whom we are permitted to hate.
It should be obvious that this must be a deliberate sinner, not a Tinok Shenishbah, or a Shogeg, or even a Chotei L’teiavon. We may only hate someone who is חוטא להכעיס. Nobody else can be described as משנאיך השם.
In Parshas Ki Seitzei (22:1-4), in the repetition of these Mitzvos, the owners are both referred to as “אחיך”, your brother.
The Meshech Chochma asks, how did my “hated / enemy” become my “brother”?
He says that permission to hate others on account of their sins is granted only to someone whose own record is without blemish. Parshas Mishpatim addresses Klal Yisrael prior to the Chet HaEigel, and so refers to the “hated / enemy”. Parshas Ki Seitzei addresses us after the Chet HaEigel, and so we may recognize only our “brother”.
So according to the Meshech Chochma, only an unblemished Tzadik may fulfill משנאיך השם אשנא. To the rest of us, ALL Jews are “brothers”.
After all, by what right do I consider myself superior to him? Do I in fact know that my own failings are of any less gravity than his? I don’t know what he’s done, or what mitigating factors may be considered on his behalf. But I am familiar enough with my own record…