'Undivided Activity', 'Zenki', harks back to some of the imagery from 'Genjo Koan': "Quietly think over whether birth and all things that arise together with birth are inseparable or not. There is neither a moment nor a thing that is apart from birth. There is neither an object nor a mind that is apart from birth.
Birth is just like riding in a boat. You raise the sails and you steer. Although you maneuver the sail and the pole, the boat gives you a ride, and without the boat you couldn't ride. But you ride in the boat, and your riding makes the boat what it is. Investigate a moment such as this. At such a moment, there is nothing but the world of the boat. The sky, the water and the shore are all the boat's world, which is not the same as a world that is not the boat's. Thus you make birth what it is, you make birth your birth.
When you ride in a boat, your body, mind, and environs together are the undivided activity of the boat. The entire earth and the entire sky are both the undivided activity of the boat. Thus, birth is nothing but you; you are nothing but birth".