Chronicle of the Righteous is about the servants, worshippers, and homes of a group of beings in Golarion (Pathfinder's campaign setting) called "Empyreal Lords." Empyreal Lords are hard to define exactly; they're divine beings that inspire small groups of worshippers (called Mystery Cults), but they're not major deities that attract thousands of worshippers and the building of major temples. They might be best thought of as demigods, because they're below deities but above normal "celestial" races like angels. That's my best guess anyway, as I'm still a little bit fuzzy on the role of Empyreal Lords in Golarion. But put that to one side: Chronicle of the Righteous is a fascinating book that has inspired me to want to integrate Empyreal Lords, Mystery Cults, and more into my campaigns. The book is a 64-page entry in the Campaign Setting line. The inside front cover is a list of approximately fifty Empyreal Lords, their alignment, areas of concern (portfolios), domains (that they grant to clerical worshippers), and favored weapons. The inside back cover is a full-page reproduction of the cover art, which is quite impressive in its own right. Between the the covers are nine sections.
1. "Tabris's Return to Heaven" (two pages): This is a dense account, written in a "handwritten" font, that tells the tale of a warrior-scholar angel named Tabris who was obsessed with fully exploring and detailing the heights and depths of the heavenly and fiendish realms. Tabris disappeared for decades before returning with his Chronicle of the Righteous, and the book contained secrets that even the celestial realms would have rather been suppressed! It's quite evocative and well-written, and surprisingly effective. It's definitely a flavourful way to start the book off.
2. " Lords of the Empyrean" (29 pages): Each of the major Empyreal Lords receives at least a half-page entry that describes them and their particular interests, along with a drawing of their holy symbol and information on what types of people worship them, where their shrines might be located, and what sorts of celestial beings act as their minions. I would say that every third or fourth Empyreal Lord receives a full-colour picture, and these are done quite well. Perhaps the most important thing in this section is the introduction of the concept of "Celestial Obedience" and "Boons." Celestial Obedience is a feat that can be taken by worshippers of Empyreal Lords and provides them with an immediate +4 sacred bonus to something like (depending on the particular Emypreal Lord worshipped) a certain type of saving throw, combat maneuver check, AC against a particular type of enemy, etc. The benefit is narrow in scope and certainly not game-breaking, but additional powers ("boons") are gained at character levels 12, 16, and 20--and some of these are pretty cool. The best part of the Celestial Obedience concept is that, although it can certainly be taken by clerics, paladins, and other divinely-focussed classes, it doesn't have to be. If your Cavalier is a worshipper of the Ragathiel, the Empyreal Lord of chivalry or your Bard is a worshipper of Seramaydiel, the Empyreal Lord of communication and music, they can gain the benefits of Celestial Obedience. It's a great way to make the gods (or demigods) meaningful to more than just clerics in a campaign.
3. "Celestrial Realms" (2 pages): This is a description of the major geographical features of the celestial realms: Elysium, Heaven, and Nirvana. I have to admit I've never had characters adventure in celestial realms, and I have no idea what it would be like to GM or role-play such a place. I suppose it's good to have something more concrete to heaven than fluffy clouds. I did like how there was mention of where mortals who plane shift to each realm are most likely to appear.
4. "Celestialkind" (6 pages): After an introduction to celestial races and a sidebar about what happens to mortal souls who reach the celestial realms ("petitioners"), each of the following varieties of good-aligned denizens of the celestial planes receives a full page description: Agathions, Angels, Archons, and Azatas. I think this would be especially useful for those pesky spellcasters who are prone to summoning celestial beings willy-nilly.
5. "Concordance" (2 pages): Although only two pages long, this is one of my favorite sections of the book. The premise is that "once an eon, and only in times of great danger or turmoil" all of the divine powers of the celestial planes gather together to reach an accord on what should be done. There's material here about the death of Aroden, Lamashtu's rise to power, hints about a deity interested in time-travel, and, most intriguing of all, "The Seventh Accord", a Concordance never spoken of in the centuries or millennia since it happened and considered so blasphemous and dangerous that no mention of it is permitted to exist. Great fodder for creative GMs!
6. "Empyreal Worship" (14 pages): This section is a grab-bag of material, but it's useful. There's a page on how the different divine classes relate to Empyreal Lords, two pages on different types of Mystery Cults (drawn broadly among themes, but useful), and two pages on "secret offerings" that can be made to improve one's chance in summoning a particular type of celestial being. Two pages are also devoted to Rituals of Mortification, which requires a character to invest a certain number of days going without food, water or sleep in order to gain both an affliction and a benefit. The actual rituals listed are said to be examples only and GMs should feel free to add more. The Ritual of Appetite, for example, requires two days' fasting, afflicts the character with a -2 penalty on Constitution checks and saves vs. disease and poison, but grants the character a +2 sacred bonus on concentration checks and Will saving throws. Other rituals are far more powerful, with one providing a +4 sacred bonus on attack rolls against evil creatures and a +4 bonus on caster level checks to overcome their spell resistance! I haven't used these rituals in play, and I'm not sure whether they would be balanced or not, especially because part of the mechanism is the infliction of nonlethal damage once a day, but nonlethal damage heals quite easy. So the idea is interesting, but I'd have to test this concept out more before I'd be confident it's a good addition to the game. Next, there's an important new prestige class introduced here: the Mystery Cultist. A Mystery Cultist gains spells at the same speed as their prior class and several celestial-themed abilities, but a big reason for playing one is that they can receive the "boons" of the Celestial Obedience feat a few levels earlier than a regular character. I'd be very tempted to try this class out, as it seems to both fit the flavour of Empyreal Lord worship and be mechanically sound. After this, here are two pages of new spells (6 in all), with specific mention that these are not restricted to worshippers of Mystery Cults (and a couple of the spells are arcane in nature). I would love to see "Charitable Impulse" in a game, as it forces someone to help others and gradually give away all of their possessions instead of committing acts of violence. Last, there are two pages of celestial-themed magic items.
7. "Lesser Empyreal Lords" (1 page): About two dozen Empyreal Lords that were, for whatever reason, not significant enough to be included in the first section receive a brief, one-sentence description here.
8. "Fallen Celestials" (1 page): Intriguing description of those celestial beings who have turned their back on the heavens, many of whom have joined the infernal realms.
9. "The Celestial Hosts" (8 pages): This is basically a bestiary. It helpfully puts into table format all of the Agathions, Angels, Archons, and Azatas introduced in other Pathfinder materials, and then describes five new ones: Cervinal Agathions, Balisse Angels, Choral Angels, Spyglass Archons, and Vernallia Azatas. I found the new creatures interesting and potentially useful (except for the Choral Angels, which were a bit too cliche for me).
In sum, there's a lot of material here and it's almost all great. I picked this book up by chance (it was half-price) and have never done much with the celestial realms in a game, but I can now definitely see why I might want to in the future; and if I do, I'm confident that Chronicle of the Righteous would be the first place I'd turn.