The gospel of salvation by grace alone in Christ alone through faith alone is presented throughout the Old Testament by many beautiful types and figures and illustrations. Some of the most precious are Abraham sacrificing his beloved son, Isaac; the Passover meal on the eve of Israel's exodus from their slavery in Egypt; and David's merciful dealing with Saul's grandson, Mephibosheth. And of coarse, the cities of refuge.
These cities were designed to provide a safe hiding place from the wrath of the avenger. Outside of the refuge you have no hope and will be killed. Outside Jesus you have no hope but will perish eternally, Acts 4:12.