The selection is a treasure. It is a collection of essays (by different authors) working through the individual religious histories of the first thirteen states. In addition, as something of a bonus, it also contains the religious histories of states that came in later—states like Vermont, Maine, Kentucky, Tennessee, Ohio, Louisiana, Missouri, and Florida.
The first thing to note is that there are some real surprises. It is crammed full of fun information.
The second thing to note is that it is a scholarly book, but still readily accessible. Whether you read it cover to cover, as I am doing, or you simply want to read up on your state, or you want it your shelf for reference, this is a great book to have.
The bottom line is that this collection of histories illustrates, in a way that cannot be denied, how the United States was a Christian republic at the Founding. Some of the states had a hard establishment of religion, meaning that there was a particular denomination that was the official denomination of that state. This would be states like Massachusetts, Connecticut, or New Hampshire. The other states had some form of soft establishment—even Rhode Island, kind of. The best example of that would be South Carolina, which declared the Protestant faith to be the official religion of the state . . . but no particular denomination.
In any case, this is a book to get.