CatholicSpirit, it’s called a “
Tefillin”. It’s in Deuteronomy 6:8 that G_D commands the Jews “
Bind them (these words) on your arm as a sign and let them be as a pendant on your forehead.” You might want to read
Deut 6:4-9 as it contains the words that are in the tefillin and the mezuzah. Jesus uses this section as the introduction to The Good Samaritan in
Lk 10:27. You can find a fuller description of the tefifllin at
Chabad.org.
This is one of the ritual laws of the Old Covenant that we as Christians, living under the New Covenant established by Jesus, are no longer required to practice. There are some Jewish traditions that I think we as Christians can practice both to honor our Jewish heritage and to gain a deeper understanding of and relationship with G_D. For example, about 10 years ago I started adopting the Orthodox practice of not spelling out “God” but using a dash or underline instead of the “o”. When I first started this practice, I had to force myself to slow down my typing to do this, which forced me to consider His Holy Name and makes the practice almost like a prayer.
As for the Lord’s Prayer, there are two ways of looking at it. First is that rabbis at the time would have prayers that they composed that were several pages long, and their disciples were required to read, memorize, and pray these prayers. When His disciples asked, “Lord, teach us to pray”, they were expecting one of these long prayers. Instead, they get something very simple and very intimate (addressing G_D as “Abba”, or “Daddy”) In addition, while the prayer is simple and perfect as it is, it also looks like it is to be a template in how we should pray to G_D: an intimate beginning, praise for G_D, a statement of hope, setting out your needs, and asking Him to protect us.