Today's reading from the Gospel is taken from Luke. Jesus was welcomed by Martha. Her sister Mary just sat beside Jesus at his feet listening to him speak. Martha, burdened with much serving, complained to Jesus that Mary wasn't helping her. Jesus pointed out to her that "Mary has chosen the better part and it will not be taken from her."
The Lord made it clear that we need to spend time listening to him. Since he is not physically present today, we need to do it through prayer. Of course, there are many other things to take care of. As long as we aim to please God by doing everything with our best effort and love, we are turning our doings into prayers. This makes "praying unceasingly" possible.