Aizen talks about the will of the hougyoku and how it isn't merely to cut down the barrier between hollow and shinigami. Basically the hougyoku has a will of its own and what it seeks to do is to understand and then create what is inside people's hearts. So it made the vaizards true vaizards because that was Urahara's wish. It gave Inoue and Chad powers because they fretted over their own inabilities. Rukia was able to give Ichigo all of her shinigami power as it was her desire due to not being free of the pain she still felt over killing Kaien.
Aizen says that now the hougyoku is a part of him he can realise that. Gin and Ichigo interrupt but Aizen says he is mostly finished anyway. While exclaiming how worthy the hougyoku is of its name Urahara attacks from behind. Aizen, Ichigo and Isshin turn to see him. Aizen: "so you came afterall Urahara Kisuke."