First of all, it is worth note that Carroll admits his bias right from the beginning, and thus honestly admits to what would have been obvious from the first few pages of his work. Among the "objective historians", the lack of bias is paramount, and is established by attacking, diminishing, and demeaning whatever subject they approach. Carroll, by way of contrast, admits a pre-existing bias, and is thus free to explore, explain, and defend his subject matter.
The Founding of Christendom accomplishes three great ends. First, it provides a succinct and riveting chronological study of the "History of the World." I admit I was quite shocked to discover that Carroll picks up his work not from AD0, but from the moment of Creation itself. Audacious! And yet his historical approach provides a new view of Genesis.
Secondly, Carroll's portrait of the evolution of Judaism, through the birth of Christ gives a compelling view of the necessity of the Old Testament as a precondition to the New.
Finally, the extent to which "Foundation" establishes chronological context is particularly impressive. Without so much as a "Meanwhile, in Greece..." Carroll manages to firmly establish the temporal relationship of Biblical events within the broader context of world history. It is one thing to look at a wall chart displaying events in different civilizations at different times, and quite another to understand the relationship between Philistine domination of the Israelites and the Homeric legends of ancient Greece. Certainly other works have hinted at the similarities between the Phillistines, Goliath and the Grecian demi-gods, but Carroll's was the first work that made it click so clearly.
Finally, this is the best of the four comparably excellent volumes for one primary reason: this volume has the least number of references to "August, the ancient dying time of Rome," the phrase of resort that may be Carroll's one true weakness.