Aligned Class (Ex)
Evangelists come from many different backgrounds, and they show an unusual range of diversity. At 2nd level, the evangelist must choose a class she belonged to before adding the prestige class to be her aligned class. She gains all the class features for this class, essentially adding every evangelist level beyond 1st to her aligned class to determine what class features she gains. She still retains the Hit Dice, base attack bonus, saving throw bonuses, and skill ranks of the prestige class, but gains all other class features of her aligned class as well as those of the evangelist prestige class.
Say my PC is Swashbuckler 5/Evangelist 10. He would have the class features of a 10th level Evangelist and a 14th level Swashbuckler (5 levels + 9 levels of Evangelist)
What happens if I take another level in Swashbuckler after that? Would I not gain any benefits from taking more Swash levels other than saves and BAB, because I've already gained the next 9 levels of class features? Or would I continue the Swash's class feature progression at level 15, as if 9 of the 10 Evangelist class levels were also Swash levels?
Evangilist stacks the extra class levels on top of the base class levels, and this works in reverse. So if you gained another level in swash, it'd be swashbuckler 15.
^^^^^^^^^^