Master Dogen said that Zazen is the dharma gate of ease and joy.
To understand what he meant we need to consider the fundamental Buddhist insight that we suffer because we believe there is a self and that there are things which belong to the self. And because we think that in our ordinary life we constellate our experience around this. Like wrapping a bandage round and round a non-existent head.
Dogen also said that Zazen is casting off body and mind, and one of the things he specifically means is that when we sit, we cast off this sense of me and mine. So experience is unwound, fills everywhere. And we can understand that suffering is not inevitable.