How often must a person inspect their tefillin (leather phylacteries worn during prayer) to make sure the scrolls inside are still intact? The Mekhilta derives the answer through a brilliant piece of scriptural comparison.
The phrase "from day to day" appears in connection with tefillin. The same phrase appears in (Leviticus 25:29), where it discusses the redemption period for a house sold within a walled city: "days shall be its redemption." In that context, the rabbis established that "days" means a full cycle of twelve months.
By applying the hermeneutic principle of gezerah shavah — linking two passages that share the same language — the Mekhilta concludes that "from day to day" in the context of tefillin also means twelve months. A person must examine the parchment scrolls inside their tefillin at least once every twelve months to ensure the sacred texts remain legible and undamaged.
This ruling reflects a broader rabbinic concern for the physical integrity of ritual objects. Tefillin are not merely symbolic. They contain actual passages of Torah written on parchment by a trained scribe. Over time, letters can fade, crack, or become illegible. The obligation to inspect them annually ensures that the commandment is performed with objects that are genuinely fit for use — not just worn out of habit, but maintained with care and reverence.