Both the Tefillin Shel Rosh and Tefillin Shel Yad, contain the same 4 passages from the Torah which record the Mitzvah of Tefillin.
In the head-Tefillin, these four passages are written on separate pieces of parchment and each passage is placed into their own compartment. This is like the Choshen, where each stone had only one name inscribed on it.
In the arm-Tefillin, the same four passages are written on a single scroll and placed into a single compartment. This is like the names on the Avnei Shoham, where all of the names of the Tribes are inscribed on the same stone.
The head and arm Tefillin also represent the idea of individuality and unity.
The head-Tefillin represents a service of Hashem based on our intellectual understanding and appreciation. The Choshen, which was worn over the heart, represents our Kavana, our emotions and feelings in the service Hashem.
In contrast, the arm-Tefillin represents action; the practical observance and ‘doing’ of the Mitzvos. This is also alluded to by the Shoham stones which were worn on the shoulders at the top of the arms.
When it comes to serving Hashem with our mind and heart, we are all different. Each person’s level, depth and type of understanding will be different and some will have greater appreciation than others. Likewise, each person will have a different emotional experience and some will have greater feeling than others in their Avodah. This is why on the Choshen, each Tribe had its own unique stone.
But when it comes to the actual observance of a Mitzvah in deed, like the Avnei Shoham, we are all on the same stone. Whether a Mitzvah is fulfilled by a great scholar or mystic or an uninspired ‘average-Joe’; whether one understands or appreciates the Mitzvah more, less or not at all, the Mitzvah and the connection achieved by it, is the same for everyone.
The Gemara teaches that there were 25 letters on each of the Avnei Shoham stones. These correspond to the 25 letters in the verse Shema Yisrael, where we pledge our absolute dedication to Hashem and readiness to sacrifice our lives for His sake. The 2 stones represent the two times we say the Shema each day; once in the morning and once in the night.
Just like the physical observance of Mitzvos is equal by every Jew, so is our Shema Yisrael. In the essence of our soul, every Jew is equally dedicated to and inseparable from Hashem Echad.
