Much of today’s daf (Nazir 6a-b) focuses its attention on the application of מִקְצָת הַיּוֹם כְּכוּלּוֹ (literally, ‘part of the day is like the whole day’) which is a halachic concept that is invoked by our Sages when discussing a variety of observances such as Nazir and, in particular, the laws of mourning when mourners often only sit on low chairs for part of the final day of shiva.
However, while מִקְצָת הַיּוֹם כְּכוּלּוֹ is generally only discussed vis-à-vis halachic observances, I also believe that it is a concept that can meaningfully enrich our life in general. For if life is like a day, then מִקְצָת הַיּוֹם כְּכוּלּוֹ comes to teach us that we should seize the opportunities that lie waiting for us within every small ‘part’ of our life. And why? Because life is fragile and fleeting – which means that we should treat ‘part’ of our life as our whole life and thereby live intentionally in any given moment. As Randy Pausch powerfully observed in his ‘Last Lecture’: “The key question to keep asking is: Are you spending your time on the right things? Because time is all you have.”
Based on this insight, perhaps this is why we apply מִקְצָת הַיּוֹם כְּכוּלּוֹ to the final day of shiva – as if to communicate to the mourner: ‘having suffered a loss, and having confronted death, your task is to live your life to the full. Seize opportunities and live each part of your life as if that is your total life, because מִקְצָת הַיּוֹם כְּכוּלּוֹ isn’t just a halachic concept; it is a message to us about how we should live our life.’