"Justice" is a big word today. But without a just God, justice doesn't make sense. Everything He does is just; justice flows from Him (Deuteronomy 32:4). Sometimes, even when we seek justice, we may face an unjust judge who loves being in office more than being truly just. But that is not the case with the Lord.
God clearly laid out laws of justice for people who accidentally killed another person. He provided cities of refuge in the Promised Land to protect them from the avenger of blood. But even though they could find safety and justice in one of these cities, they could never live down the fact that they had taken a human life, even if it was unintentional. These cities were a place of the Lord's mercy, but they also showed that He does care about the sanctity of human life.
The only reason we are still alive is because God is merciful to us, even though our hearts are evil. Jesus taught that even hating our neighbor or getting angry with him puts us on the same level as a murderer. We all have real guilt, and so we need a City of Refuge to flee to! The good news is that Jesus died in our place. He – the Just One – suffered for us who are unjust. And because the Lord laid our sins upon Him, we may now walk in the freedom and liberty that He has bought for us by His death and resurrection!