וכי יהיה איש שנא לרעהו, "And if there will be a man who hates his fellow, etc." This paragraph alludes to what is taught in Makkot 12 that the guardian angel of Esau, i.e. Samael, will make three errors of judgment in the future. One of them is that although the cities of refuge will provide refuge only for someone who kills inadvertently, this guardian angel is under the impression that such cities also provide refuge for intentional murderers. [The Talmud deals with an interpretation of Isaiah 63,1 assuming the prophet refers to the guardian angel of Edom, i.e. Samael who also mistakes the city Bazrah for Betzer (spelled similarly in Hebrew) and tries to take refuge there. Ed.] כי יהיה לאיש שונא, the worst enemy a person has is his evil urge, he is the root cause of all feelings of enmity. לרעהו, "against his fellow," i.e. that he represents himself as man's friend whereas in reality he means to harm you. He uses the pretense of loving you as a means to harm you. וארב לו, "and he ambushes him," i.e. he causes him to sin. You must remember that the first sin a person commits is considered as if it had been inadvertent. Having committed that sin, however, he thereby provides the evil urge with access to his soul as we know from Genesis 4,7 "that sin crouches at the entrance (to your soul)." As long as man has not sinned the evil urge is till outside the entrance. Not only that, but Satan tries to convince you that what you thought was evil is actually good. This is the worst kind of ambush one can be exposed to. The Torah continues וקם עליו, "and he rises up against him," i.e. once he has caused you to sin he now confronts you openly whereas previously he was treading very carefully, so that you almost did not notice his presence (compare Sukkah 52).
והכהו נפש, "and he kills someone, etc." the reference is to Samael who injures man's soul because sinning leads to the death of not only the body but eventually to the death of the soul. ונס אל אחת הערים האל, "and he flees to one of these cities;" if he flees to one of these cities of refuge, i.e. Betzer which is one of them, ושלחו זקני עירו, "and the elders of his town have to send messengers there" (to bring him to justice). This is a reference to the Celestial Court which is known as the city of the guardian angel of Esau. ולקחו אותו And they will take him from there and hand him over to the redeemer of blood, i.e. to God Himself.
ומת, "and he shall die." Here the Torah alludes to a mystical aspect of Sanhedrin 38 that God pointed His small finger at several groups of the angels who opposed the creation of man, and that He burned them. ביד גואל הדם ומת, "in the hand of the redeemer of blood and he will die." This means that God will strike him dead, not the relative of the deceased. Seeing that our sages have said that Samael [the angel of death, -compare the Chad Gadyah song in the Haggadah shel Pesach Ed.] will be killed also by the Israelites who will combine with God to kill him, the Torah adds לא תחוס עינך עליו, "you must not have pity on him." Although the righteous have derived benefit from the existence of the angel of death [having received credit for resisting his temptations to sin. Ed.], they have to counterbalance this benefit against the many occasions when the angel of death spilled the blood of innocent people through making them guilty by lying in ambush for them. As a result of his death, וטוב לך, "it will be good for you;" once the spirit of impurity is abolished the good on earth can become complete in the proper place, i.e. within the hearts of the Israelites.