Halakhah su Deuteronomio 33:9

The root of this commandment is well-known, as the tribe of Levi was from the select of the tribes and prepared for the service of the House of God, and [so] they did not have a portion with Israel in the inheritance of fields and vineyards. But they nonetheless needed cities for them to dwell in - they, and their children and their infants and all of their animals. And because of the greatness of their stature and the fitness of their deeds and the 'grace of their worth,' their land was chosen over the lands of the other tribes to shelter any one that kills by mistake - maybe their land that is sanctified with their holiness would atone for him. And there is another reason in the thing: Since they are people of known [character] in virtues of disposition and respected wisdoms known to all, they would not loath the killer being saved with them and they would not touch him; and even if he would kill one of their friends or redeemers (relatives) - since he killed him 'suddenly and without enmity.' And about this select tribe is it stated (Deuteronomy 33:9), "Who says about his father and his mother, 'I have not seen him'" - meaning to say, that they will never do anything besides [that which is from] the proper path and in line with the truth; and even [in spite of] the love of father and mother and brothers and sons, which is obligated and compelled by nature, and all the more so [regarding] the love of other people. And I have further written another argument about the matter in the Order of Behar Sinai (Sefer HaChinukh 342).