Exodus 13:9
And it shall be for a sign unto thee upon thine hand, and for a memorial between thine eyes, that the LORD’s law may be in thy mouth: for with a strong hand hath the LORD brought thee out of Egypt. And it shall be for a sign unto thee upon thine hand, and for a memorial between thine eyes, that the LORD’s law may be in thy mouth: for with a strong hand hath the LORD brought thee out of Egypt.
The ordinance was to function as a mark upon the hand and a reminder set before the eyes, keeping the divine law present in thought and in speech. Its purpose was to hold continually before Israel the fact that the Lord had freed them from Egypt by the strength of His hand. That mighty act of liberation was therefore bound together with obedience, so that remembering the deliverance would keep the law in the mouth.
The strong-handed deliverance embraced God's guarding care over Israel throughout their journey out of bondage. It included the crossing of the Red Sea, when the people passed through under divine protection. That guidance and protection were exercised under the leadership of Jesus Christ, present with Israel in the pillar of cloud.