What a picture Dōgen paints of the deep interconnection and identity of everything, including our lives! Here he describes how life is a field of opportunity, and how it is up to us to make something of it. Of course, we are not totally free to do and be what we want, no more than a fish can leave the water or a bird can fly without the air. Nonetheless, where and how the bird or fish travel within their given medium, and with what grace and energy, is largely up to them.
Thus, practice never stops because the features and variety of our lives never stop, so we practice right here where we are. In this place and setting, in this facet of the whole, our practice brings life to life. This is the sea in which we sail or swim, the stage upon which we dance, the sky where we fly. The dancer brings the dance to life by being the dance. We are the life of this earth, and like the fish in the water and birds in the sky who bring water and sky to life, all this world is our extension, not merely our location.
This is your place, your life right here, and you cannot be anywhere other than where you find yourself so long as you are alive. So please live this life well and experience this place wisely. The possibilities, if not quite endless, are greatly up to you. We human beings cannot change all the circumstances in which we find ourselves, but within our realms we have more power than we know to range freely. Please swim or fly your course with grace and skill.