Yom Kippur (Day of Atonement)
Jewish tradition prescribes a complete fast: not even water, and many won't even brush their teeth. That's not explicit right in this passage, which says only, "You shall humble your souls." And indeed Rabbi Israel Salanter, generally considered the founder of the Mussar (ethics) movement in Orthodox Judaism, commanded his congregation to eat on Yom Kippur during a cholera epidemic to prevent weakness and save life, and he ate before them in the synagogue.
But "no work at all" is very clear, and so it is certain that no work at all is at the heart of humbling our souls. As I was thinking about this today, I saw clearly that our work indeed feeds our pride, which is what we like about it the way some like fine cocaine or crystal meth. Work can easily make us high and full of ourselves. That is why atonement and our work are totally incompatible, just as Torah teaches here. Our own work is what we chiefly need to repent of, and the pride it nurtures in us with its related contempt for others who don't work as hard as we do.
The Pharisee praying with himself in the temple is lifted up in his heart by his work, and how it is better than the tax collector's.
Finally, although we are to do no work at all, one work is permitted, and indeed required - circumcision on the 8th day. Circumcision isn't our work to be puffed up about. If it's real, it's God's work done by God's knife (Jeremiah 9:26). The only way we can do no work at all and humble ourselves is if God works. He's always doing mercy. Thus Rabbi Salanter was late to synagogue and missed the Kol Nidre prayer because he stopped to take care of a baby that had been left alone in a house on the way. Justice and mercy are God's work, not ours, so we need to be doing that when we're supposed to do no work at all.