John Wesley on Numbers 35:6

Cities for refuge - Or, of escape for manslayers: And these cities are assigned among the Levites, partly because they might be presumed to be the most proper and impartial judges between man - slayers, and wilful murderers; partly because their presence and authority would more effectually bridle the passions of the avenger of blood who might pursue him thither; and perhaps to signify, that it is only in Christ (whom the Levitical priests represented) that sinners find refuge and safety from the destroyer.