Every little detail of the Divine Comedy has been worked out and planned with the utmost precision. The ninth abyss is no exception. The splitting of the men fits into the pattern of the rest of the punishments in the inferno. These men who reside in this pouch are sowers of discord and schism. To sow means to disseminate or spread throughout the land.
Schism means division.
Thus, the physical punishments literally express the philosophical sin. As Dante watches the man who has just been split into two, the man looks back at Dante. And as the man turns his attention to Dante, so do we. The man has a strange pride in splittng himself open. Dante also takes tremendous pride in describing this scene, which he first claimed was impossible to ever put into words.