Mezuzah(Deut. VI, 9), literally translated as "doorpost" is a piece of parchment which has written on it the very holy prayer of the "Shema" and other prayers. It is placed in a case, which comes in many shapes and sizes and is affixed to the door post of a Jews home or office.
The mezuzah whereby the words of God are written on the door-post of every Jewish home is meant to remind the occupants, on entering their home and on leaving it to go into the world without, of God's constant watchfulness and guardianship.
Through the ages the Mezuzah has been part and parcel of Jewish Life. The Torah teaches us that it serves as a protection and a guardian for one who affixes it to his doorpost.
Torah, is something which can be learned by one who has the skill or one who puts himself to it. Tefillin, can be worn only by men and after the age of 13.
The Mezuzah is special because it is placed on the door-post for every one to see and to gain blessing from.
The Talmud tells the following tale to depict the greatness of the Mezuzah.
When Onkelos the son of Kalonymus became a proselyte, the Emperor sent a contingent of Roman soldiers after him, but he enticed them by citing scriptural verses and they became converted to Judaism. Thereupon, the Emperor sent another Roman cohort after him, bidding them not to say anything to him. As they were about to take him away with them, he said to them: 'Let me tell you just an ordinary thing: In a procession the torch lighter carries the light in front of the torchbearer, the torchbearer in front of the leader, the leader in front of the governor, the governor in front of the chief officer; but does the chief officer carry the light in front of the people that follow? 'No!' they replied.
Said he: 'Yet the Holy One, blessed be He, does carry the light beforeIsrael, for Scripture says. And the Lord went before them … in a pillar of fire to give them light.' Then they, too, became converted.
Again he sent another cohort ordering them not to enter into any conversation whatever with him. So they took hold of him; and as they were walking on he saw the mezuzah which was fixed on the door-frame and he placed his hand on it saying to them: 'Now what is this?' and they replied: 'You tell us then.
Said he, 'According to universal custom, the mortal king dwells within, and his servants keep guard on him without; but in the case of the Holy One, blessed be He, it is His servants who dwell within whilst He keeps guard on them from without; as it is said: The Lord shall guard thy going out and thy coming in from this time forth and for evermore.' Then they, too, were converted to Judaism. He sent for him no more.