The right hand represents Buddha (Kongokai) and the left hand represents human beings (Taizokai). Taizokai is the transforming period of something we can't see to something we can see. Someone deceased, for example. The body is gone, but memories and some aggregated data inside of the body will be passed on through memory- implanted and transferred to someone else around that person. Data collected, reformed, and then passed through legends in written or verbal form in the future. We are receiving Buddha's intelligence and we are summarizing what we earned through the chanting, through life. We are going to be Buddha later. There are two Buddha- ourselves, and someone who is granted, who is assigned, or named by someone who is now reaching the Buddha level. History always comes around. As long as we think we are Buddha as human beings, we need someone as Buddha. Right hand represents future and past because there is no physical form. Left hand always represents this present moment. Shingon tradition always crosses the fingers into kongo-gassho because we are experiencing the time travel. Without someone remembering anything or anyone in the past, that person's legend is never proven, so we always try to match the present form and the future/past forms together in the Shingon hand gestures. Shingon tradition is vertical, which means any secret must be kept inside of the community because someone who really wants to be a member of the community has to have engagement with commitment and oath to be a member of the society, because the asset and culture is the treasure. Friendship, love, respect.
Inside of the hand gesture, we need some space, because the Buddha exists within the space.