Mishpatim

This parsha deals primarily with civil law & how one should treat other people. It gives practical guidance on the application of these laws so one can know how to live even the mundane parts of his life with Torah guidance. One of the laws is כי תראה חמור שונאך רובץ תחת משאו , when you see the donkey of your enemy crouching under its burden, you should help him.
The משך חכמה asks why in our parsha it says to help the donkey of your enemy while in Sefer Devarim, when talking about the same thing, it refers to it as חמור אחיך your friend’s donkey. Why the change?  

His explanation cites the gemara which asks how is it possible for one Jew to hate another, to even have this concept of שונא. It answers that the Torah is talking where one saw the other sinning so then it’s permissible to hate him.

The משך חכמה continues that that concept applied only before the sin of the golden calf,when the Jewish people were on a very high level & all were very holy. Then, if one saw someone sinning, he had the right to hate him. However, after the sin of the golden calf when the people's level declined drastically, if one saw someone sinning he should first check his own deeds for he would certainly find faults; he then had no right to hate anyone else. Therefore, when it’s before the sin, as in our parsha, it states your enemies while in Devarim, which is after the sin, it says your friend because who among us is so pure to even have enemies.
That being said, even if we're allowed to hate someone who sins, what's the significance of telling us that you have to help specifically him?

The Midrash brings a story of two donkey drivers who hated one another that were going on the road. As they were traveling, one of them passed the other & saw that his donkey was falling under its heavy burden. Since he hated that driver, he just kept on going without helping him. After a few minutes he began to feel guilty, thinking to himself that the posuk says if you see your enemy’s animal falling under its burden you have to help. Yet, that's just what I did; I passed my enemy without helping; how can I transgress the Torah?

So he turned around & started to help him. Then the enemy thought to himself, “hey, I thought this guy hated me; I see he really likes me; he's helping me. They went to the inn afterward for a drink & became good friends. What caused them to make peace/ - listening to the Torah, because it specifically said enemy.   

This is alluded to in the targum when אונקלוס adds a few words instead of just translating the end of the posuk which says עזוב תעזב עמו , which means you should continuously help him. He adds in משבק תשבוק דבלבך עלוהי ותפריק עמיה , throw away what's in your heart & unload with him. The whole point is for you to take any animosity you have toward another person & get rid of it. Then do the work together with him as friends.

The Torah teaches us not to judge others until we’re perfect & then rid ourselves of any hatred we might feel toward someone else. By going out of our way for someone we might not like we’ll see that the feeling of hatred will go away & love will take over, enabling the coming of Moshiach speedily in our day!