When we breathe, we do not stop inhaling because we have taken in all the oxygen we will ever need, but because we have all the oxygen we need for this breath. Then we exhale, release carbon dioxide, and make room for more oxygen. Sabbath, like the breath, allows us to imagine we have done enough work for this day. Do not be anxious about tomorrow, Jesus said again and again. Let the work of this day be sufficient.
Source: Sabbath, Restoring the Sacred Rhythm of Rest by Wayne Muller