User blog comment:Jopjopjop/High School DxD BorN episode 3 review/@comment-3290441-20150420184913/@comment-26209278-20150420222810

Yea, exactly, he didn't have the physical power to bring out his BB, he had to use the sacrifice to achieve it. Just like he sacrificed his arm for the Raiser fight. He didn't have the strength to attain it, and had to give up something for it in return.