236. Therefore, there exists a limit to the scope of the physical body. And the nearer we approach this limit the clearer it is that details of physical life are being shown as "nothing", which is due to the physical body's failing usefulness. But this is actually caused by the fact that we, as previously mentioned, find ourselves nearer and nearer to the outermost boundaries of the physical world, on the threshold of another world, in other words a different form of existence. As this form of existence, as mentioned above, cannot be physical, it will be defined as spiritual. This spiritual existence is experienced under quite different conditions or dimensions of sensing from the physical one, and can be experienced only by spiritual bodies. The physical body is built only as a tool for a concentration of consciousness which consists of time and space, and in this way is completely useless for a form of consciousness, the dimensions of which lie outside those two realities. Just as a fish's body is built for promoting life in the water and a bird's for life in the air, so is the human physical body built to promote life in time and space. And as the limit of the surroundings in which the fish moves is water, so are time and space also limits to the conscious life of a living being who is still sensing only by the power of the physical body.