“A sign on your hand and a symbol on your forehead”
So it shall serve as a sign on your hand and a symbol on your forehead, for with a mighty hand the LORD brought us out of Egypt. (Exodus 13:16 BSB)
What it sounds like today
A figurative call to keep God's acts in mind.
The cultural key
Taken by many as pure metaphor, this command (repeated in Deuteronomy 6:8; 11:18) was understood in Judaism as a literal instruction, and it gave rise to the practice of tefillin, or phylacteries. These are small black leather boxes containing hand-written parchment slips of Scripture (including this passage), which observant Jewish men bind with straps onto the upper arm, so it rests near the heart, and onto the forehead, between the eyes, during weekday morning prayers. The idea is that God's mighty deliverance and His law should be bound to one's actions ('on your hand') and one's thoughts and sight ('on your forehead'), kept constantly present rather than merely recalled. Jesus refers to these boxes when he criticizes those who 'make their phylacteries broad' for show (Matthew 23:5). A modern reader hears a figure of speech; the first hearers, and Jews ever since, saw the origin of a tangible daily practice.
Recovered meaning
This command is the source of tefillin (phylacteries), small Scripture boxes bound on the arm and forehead in prayer, so that God's deliverance and law are literally kept on one's hand and before one's eyes, not just remembered.