A mourner is obligated in all mitzvot except for one: tefillin. Why is he exempt from wearing tefillin on the first day of mourning?
The Sages explained that tefillin are called pe'er — splendor or beauty. When Ezekiel was instructed not to observe the usual mourning customs after his wife’s death, he was told: “bind your splendor (pe'ercha) upon yourself” (Ez. 24:17). Despite his personal loss, the prophet was commanded to keep wearing his beautiful tefillin.
Similarly, our custom on Tisha B'Av is not to wear tefillin during the morning hours, when our grief over the destruction of the Beit HaMikdash is the most intense (see also Mishneh Torah, Laws of Fasts 5:11). Why is wearing tefillin inappropriate in times of mourning?
The key, Rav Kook explained, lies in the description of tefillin as pe'er. Beauty is meant to make an impression on others. When we perform a mitzvah in a beautiful way ("hiddur mitzvah"), we intend to engage our emotions and sense of aesthetics. By speaking of the spiritual beauty of tefillin, this indicates that they have the potential to inspire and make an impact on others.
This aspect of tefillin is supported by Rabbi Eliezer’s explanation of the verse:
“All the nations of the world will see that God’s Name is called upon you and they will be in awe of you.” (Deut. 28:10)
In what way will the nations of the world see that “God’s Name is called upon you"? Rabbi Eliezer in Berachot 6a explained this in a literal fashion. He taught that the verse refers to the tefillin worn on the head. Tefillin, containing passages from the Torah mentioning God’s Name, are a visible sign for others that ‘God’s Name is called upon you.’ Rabbi Eliezer saw tefillin as a vehicle for influencing and inspiring others — “they will be in awe of you.”
How does this explain the Halachah that mourners do not wear tefillin?
To influence others, the soul must be in a state of strength and joy. By utilizing our inner joy, we are able to show others a path of enlightenment.
Bereavement and sorrow have their place; there are times when one needs to mourn. But when the heart is heavy with pain and grief, one cannot reach out to others. It is wrong to influence others while embittered. No good will come from spreading sadness to others.
For this reason, when one is overcome with grief and sorrow, it is not a suitable time to adorn oneself with tefillin and their spiritual splendor. It is a time to draw inwards, not radiate outwards. We should wait until God dispels the darkness and we are able to return to Him with the complete teshuvah of love. Then we will may reach out to others and illuminate them with a path of light and joy.
(The Splendor of Tefillin. Adapted from Ein Eyah vol. I, 1:157 on Berachot 11a)