Why is the text so blurry

Having negative piety gives you a bonus to technology rate and taxes, which is how you get the tech rate. There is no unmentioned bonus. Ideally you want to keep piety at one end of the spectrum or the other, both have advantages. Piety is not like Piety in crusader kings, where it is all good. Instead it represents the advantages of secularism (tech, church taxes) versus theocracy (morale and stability).

You can see your current modifiers by hovering over the Current Piety label or percentage slider on the Religion tab. Hover over the flag icons on either end of the slider to see the maximum available modifiers.

I believe Marrakech is the capital province. It's hard to see in your photo, but I think you will see a crown on top of a pole coming out of the map in that province -- that indicates it is a national capitol.

You would receive that province as part of a full annexation, but you can't just take the capital as if it were any other province.