Master Dogen describes Zazen as dropping off body and mind. That is, dropping off this sense of a me and things that belong to me. It is his way of describing anatta.
He doesn’t say that dropping off body and mind is a preliminary to the real activity of Zazen, but that Zazen is the continuous dropping off of body and mind. The activity of Zazen is this continuous activity of dropping off. It is an activity, not a state. It is an orientation, not an attribute.
He also says, although he attributes this to his teacher, Nyojo, that when body and mind are dropped off, we are free of the five desires and the five hindrances. The five desires correspond to the desires of the sense organs. The five hindrances are desire, ill-will, laziness, restlessness and doubt. If we think that practice is the vehicle for our own aggrandisement, we are full of these hindrances. But if there is no me and nothing belonging to me then where can these hindrances attach?
Hence, Zazen is the dharma gate of ease and joy.