Inquisitor Spells take standard actions to cast just like all the other spells.
Inquisitor Spells take standard actions to cast just like all the other spells.
I believe he was refering to the Litany spells, which only require swift actions. Granted, the inquisitor's swift actions are very sparse as is.
I was thinking along the lines of what blackbloodtroll wrote...
You could potentially not take any Barbarian levels and just gain Rage thru Inquisitor levels.
That lets your Inquisitor casting advance alot faster, and even gets you more Class Abilities if you care about that.
BUT...
If you look at the Anger Inquisition, you realize that Anger never grants any Rage Powers, and since having the Rage POWER Class Feature is necessary to take the Extra Rage Power Feat, you will never have any Rage Powers... which kind of sucks. You also don't gain Rage until 6th level of Inquisitor (and you are Raging like a 3rd level Barbarian), so you need 6 levels of Inquisitor to even think about that. Remember, Rage Prophet doesn't gain the ability to convert spells into Rage Rounds until 6th level of Rage Prophet, and isn't advancing Rage Rounds besides that, so relying on the # of Rage Rounds that a 3rd level Barbarian would have seems rather low.
With the Rage Sub-Domain, you will have to wait until 8th level of Cleric in order to gain Rage (as per a Barbarian 1/2 your Cleric level), but you eventually gain a Rage Power (with no Barb-level Pre-Reqs) if you take *12* CLERIC levels. I'm not sure what RAW/RAI is there, but I would count that as having the 'Rage POWER Class Feature' at that point, since it's coming from a Class Feature, even if subsumed under the Domain Class Feature.
...All in all, taking at least 2 levels of Barbarian, to get the Rage Power Class Ability (allowing you to take Extra Rage Power Feats) seems a better deal for MOST Rage Prophets who are interested in getting the most out of Rage. Many levels of Barb puts you closer to qualifying for nice 8th-Barb-Level Pre-Req powers down the road, and the Rage Rounds are nice to have. The Cleric approach seems doable for Caster-heavy Rage Prophets (you don't per se need all 12 levels of Cleric up-front, just 8 levels to gain Rage, so you can dip back into Cleric to qualify for Rage Powers down the Road).
If you are interested in Inquisitor for it's Swift Litany Spells, it seems like you would want to advance in that Casting as much as possible... especially since Rage Prophet is only partial Casting Progression. Dipping 2 levels of Barbarian would fix the Rage Power issue, but your Rage Rounds are going to be rather hampered by that, so much that you kind of would need to still take 6 levels of Inquisitor (for net Rage Rounds equivalent to 5th level Barb at 8th/9th Char Level before entering Rage Prophet)
I wanted to Edit my previous post, but ran out of time...
As I see it, Rage Prophet pretty much does depend on you getting good value out of it's Partial Casting progression (unlike Dragon Disciple, for example, where it's giving you lots of stuff that doesn't depend on Casting, almost all of Rage Prophet's effects apply to Casting, as well as to scaling Rage Powers). Progressing in a 3/4 Casting Class like Inquisitor is watering it down further, although if you consider early entry/ unique options like Swift Litanies, maybe that is still OK for you... But in that case, *I* would definitely want to be as progressed as I can in the base class, unlike the OP's 1st post which only takes 1 level in Inquisitor.
So... I would consider whether it might just be better to progress Oracle or Cleric casting, and use Quicken Feat/ Rods to get that Swift Action economy*. For Cleric Casting, I would take at least 2 Barbarian levels, and thus not depend on Cleric Class levels for Rage (although taking 8 levels of Cleric with Rage Sub-Domain, or only 6 levels if you take the Anger Inquisition which is open to Clerics also, would let you synergize for Rage Rounds and Rage Power scaling).
As an aside, given heavy multi-classing like the OP's build, I think it would be reasonable to have a Feat that granted the Oracle Curse class Feature - Perhaps giving a minimum Oracle Level of 1, but no other benefit: except that it lets you avoid dipping in 1 level of Oracle just to get your Curse, it otherwise functions the same: non-Oracle levels count 1/2 towards advancing the Curse. If you aren't going to progress Oracle Casting, it seems silly to me to dip 1 level in the class when you are going to progress Cleric/Inquisitor/Druid Casting. Since taking such a Feat pretty much comes with negatives as well as positives, I don't see such a big problem balance-wise, and it's just bypassing a 1-level dip for the Rage Prophet pre-reqs anyways.
* You should also just think of ways to better use Standard Casting economy... Some spells include a Touch Attack, for one. You can also Cast, then Move, putting yourself in position to take an AoO. Getting melee Full Attacks isn't something that you should be routinely getting ANYWAYS, so the hit to action economy isn't all that bad. Pre-Casting outside of combat/ Cast+Maneuvering as I described are both good ways to use your Casting ability... Since you Multi-Classed AND Rage Prophet is only partially progressing Casting, you don't really have the spell slots to be Casting every round of a battle ANYWAYS, so it isn't really much of a restraint on you over-all to follow the above advice, IMHO.