The Accursed Thing

What could be so sinful that the LORD would condemn them so severely for their sin? How is the holiness of God on display, not only in condemning Jericho but all that was in that city? Why was the city accursed? How does God's sentence that any who rebuilt the city would do so with the death of their firstborn, serve as an anti-type of God laying the foundation of salvation in the death of His Son?