This work invites a lot of comment on many subjects. Given that I have been through several of Paine's earlier works, it should be first noted that he was a person whose every opinion was so self evident that anyone who disagreed was guaranteed to be deficient in their mental faculties. This is all part of his extended world view, which is that his generation is the first to have encountered the phenomenon that we call "reason", it having been completely unknown to all prior generations. Everything else derives from this.
One thing that Paine highlights is that the only things worth studying are science and technology. Based on that viewpoint, I should have tossed his work away early on, especially since I am a technologist by profession, but I have persevered on in spite of this being a waste of mental resources. We find that all ancient writings are mythology or errors, so we have nothing to learn from them, while Paine's generation had rediscovered, embraced and extended science, which was previously invented and known exclusively by the ancient Greeks. A corollary is that there is nothing to be gained by studying dead languages, so only a handful of linguists need concern themselves with these matters. Since Monarchy comes from ancient times, it is clearly wrong and needing to be reformed. The same applies to religion. His fury, however, is exclusively directed at Christianity, so the later half of this work is dedicated to proofs of the fabrication of the Bible. For example, he clearly proves that the author of the book of Judges was not named Rabbi Judges, thus, this work has no authority. This is so self evident that only a moron would disagree, and for making this great discovery, Paine is deemed a "philosopher".
My own opinion is that Reason has always been with mankind, this having been given to us by God. The problem is that Reason is morally neutral, so that it can be employed for either good or evil, or to pass on truth or falsehood, depending on the character of the one who employs Reason. It is Paine's failure to observe this most basic, self-evident truth that places him and his like-minded intellectuals purely into the class of Sophists, while entirely excluding them from the category of Philosophers. So there.
A final point that I will note is that Paine calls himself a deist, while crediting his parents for giving him a good moral teaching from the Quaker religion. Yet at the same time, he expects to live after the grave, while having no expectation of judgment for sin. This seems to me to be just one step removed from Quakerism, since this religion was always closer to deism than to Christianity. He wants to credit Jesus as a moral teacher, while rejecting any teaching that he doesn't like as being fraudulent. The inconsistency in all this is his belief that deism is inherently superior morally to Christianity, yet acknowledging the moral upbringing that he owed to Christianity. In the end, this sort of deism is doomed to moral decay, as it has proven, while at the same time it boasts of its morality more than any other religion.