In the daily binding of tefillin, the physical and the metaphorical align. We recite the in the first paragraph of the Shema (Deuteronomy 6:8):
וּקְשַׁרְתָּם לְאוֹת, עַל-יָדֶךָ; וְהָיוּ לְטֹטָפֹת, בֵּין עֵינֶיךָ
Uqshartam le-ot al yadekha, vehayu letotafot bein einekha
Bind them as a sign on your arm, and wear them as frontlets between your eyes
Never mind that we don't know what "totafot" (here translated as "frontlets") are. Perhaps the words of the Torah are to be taken literally, as an instruction to actually attach these words to our arms and foreheads. Or perhaps the image simply suggests the devotion of mind and hand, i.e. thought and deed.
Regardless, the tefillin that we wear in the morning remain with you all day, long after they are physically removed. This sign of devotion to the Torah begins with the concrete and continues metaphorically all day, a unity of the spiritual and physical.