Fr Kirwan's book is a good introduction to Rene Girard. Reading Girard's theory on mimetic contagion and scapegoating and its application to the Old and New Testament is a revelation. Girard sees the revelation of God in the Old and New Testament as not just another myth but rather the process by which God unfolds what has been going on in Human Culture since time began. For Girard, all human cultures are founded on a scapegoat who has been ritually murdered. Myth tells the foundational murder from the perspective of the vitimisers. Girard discovered that, by contrast, the Judeo-Christian scriptures do the opposite: they side with the victim.
However, having read Kirwan, it is always best to go back to Girard and let him speak for himself.