Why was the Espada build?

Answer 1

Well, this is very complex question i try to answer, if you're update to the manga then you probably understand what i actually mean.

Ok the espada, first the espada was built for the winter battle that will take place in Karakura town. Which is where Aizen plans to make the Ouken there. The gotei 13 will try to stop Aizen from succeeding. In order for Aizen to battle the gotei 13, (we all thought) that espada will there to battle to them.

However, since the deaths and defeats of 5-9 in Hueco mundo, Aizen uses the remaining the survivors of the espadas to take to Karakura town to battle the Gotei 13 they were espada rank 1, 2 and 3.

During when espadas battle the captains (except for the General commander) that went to battle in Karakura town, they successfully did weaken the Gotei 13 because of the intrusion of Wonderweiss.

So you could say Espada was built to weaken the Gotei 13 but later in the manga is when the role of espada becomes confusing or pointless.

This best answer i can think of because of the latest issue in the bleach manga.