In Jewish tradition, there are two ways that people would put the instructions of the Shema into practice in a tangible fashion. The Shema is a portion of the Jewish law from Deuteronomy 6:4 - 9 which states that God's commandments should be tied "as symbols on your hands" and should be bound "on your foreheads." In addition, God's people were to "write them on the doorframes of your houses and on your gates."
Phylacteries were the way Jews would literally bind God's commandments on their hands and foreheads. These small square leather boxes were tied on the arms or foreheads, usually during prayer time, but might be worn all day long. Specific passages of scripture were written on little scrolls inside the boxes. These boxes are also called tefillin (see link below). In chapter 5, Daniel goes to Capernaum to visit Joel, and in the city "he saw four elders of the Pharisees, the phylacteries bound to their proud foreheads."
A mezuzah was the way Jews carried out the command to write God's commands on their doors. A mezuzah is a small case in which the Shema is written on a small scroll. If a person can't afford the case, just a paper with the words on it can be stuffed into a crack by the side of the door. Both the writing and the case can be called a mezuzah. Anytime a person comes into the home, he or she touches it to acknowledge the truth of God's commands and one's submission to God alone. In chapter 3, when Daniel visits his home, he "touched his finger to the mezuzah, the little niche in the door frame that contained the sacred verses of the Shema."
Wearing phylacteries and touching the mezuzah were ways to make God's presence tangible and to keep God's commands always in the minds of his people.