As "gross" as stream-entry is, with unwholesome mental states still quite capable of arising, at least that mind has found the truth and can't help but be honest with itself. It would also seem that after this point, since the mind is firmly rooted in reality, the process of conditioning toward Nirvana is mostly on auto-pilot, as if the mind is being pulled instead of pushed toward the goal. It's the only real direction that the mind can go;