We cannot truly know who we are and be who we are at the same time. For further explanation see who we are . Also, one idea is deemed more reasonable than another idea if it is more consistent and sound. So we have no way of consciously identifying who we are except through limited representation.
Form refers to the fundamental basis for things.
Knowledge refers to conscious meaning in the form of symbols. We are consciously aware of thoughts. We must exist. In order for us to exist, there must be a being or basis behind our existence. Our sensory information, in the form of our sensory receptors' responses to external stimulus, implies an indirect relation with the external world.