You don't have to tell them everything
First, just because there is some lore about something in the campaign book doesn't mean the players have to know about it. I remember playing this very campaign as a player, before reading some parts of it, and there was a ton of detail that could have been skipped without it being an issue.
Remember your goal as a GM is not to feed your players with the contents of this book, it is to make them live an adventure! The book is only here to help you achieve that.
What you should tell them about
To be able to get interested in your campaign in the first place, players should have access to general info, and this you can give them before the first session: what is the goal of the Crusade, why Kenabres is an important strategic point to hold, the name of Galfrey, maybe some other famous crusaders like Staunton, some of their deeds they are famous for... This is an opportunity for them to use this info for character creation! ("what if I played a silver dragon lineage bloodrager whose bloodline received the benediction of Kenabres' protector?" -> you can be sure this character will be extra-motivated to kill demons after the first session.)
During game you should definitely take time to tell lore about stuff related to their character (let's say one in an alchemist, then the infos about how nahydrian elixir has been invented would probably interest them, even if they don't plan to make some themselves). But you should also answer their interrogations when they get interested in something specific: in our campaign nobody cared about Soziel and thus we barely knew he existed, while a random mongrelman not even named in the book took a disproportionate importance.
And finally, there is background that needs to be told for players to be able to follow the campaign. For example when they get the order to recapture Drezen, they need to know why Drezen have fallen and why this time the crusaders are going to be able to hold it. Same goes for many of the sidequests, like recovering the Suture: a minimal amount of background is needed to know why the character are doing this instead of something else.
In the end the ideal amount of lore-dropping will highly depend on who your players are, so there is no perfect recipe that will work for all groups. Some players don't mind spending ten hours on a single 5-rooms dungeon as they try to have all the possible information on everything. Some have enough with just the bare minimum, and anything extra is boring.
How you can tell them about
There are many special techniques to tell the players (printing it and giving them as a prop, reading a text aloud, giving the text to read to one player...) that can all be interesting but will also all become boring if overdone. What I want to focus on here is about how you can tell the characters.
Found text, as if the description was actually something written in the game world, is usually very efficient. Characters can choose to read it or not, and spend the amount of time they want doing so. This text can be a letter (sent to them or intercepted), a diary, a book... This carries the specificity that characters won't be able to interact with it: they can tear the paper in anger but the paper is not going to give them the missing information even if they do so.
Monologues often feels more artificial. Characters want to react when they are talked to, not just sit and listen. I find usually more efficient if I go this route not to read anything: the NPC answers their questions, and adds stuff to point them into asking about what they still have to learn. Anyway it will require you to improvise when they ask for things you haven't anticipated.
A variant of a monologue is a story narrated by a NPC. This works well for downtime: everybody is chilling at the tavern with a NPC they like (but whose they don't know yet the backstory) and a bard comes up and sing something about their deeds.
The cheat code
Finally, there is also a technique that as far as I know everyone GM uses, knowingly or not. Once you know a specific piece of lore will never get uncovered or has become useless (eg because if was about a monster the PCs have already killed) you can tell the players without telling the PCs, outside of a game session. Sometimes even years after a campaign has ended I have my GM tell me something like "by the way, remember that dragon the final boss had as a pet? Well actually the eggs you saw on the house of the archeologist on 1st arc are his sisters and brothers".