Affixing a mezuzah on the doorpost is much more than a tradition. Indeed, this practice is mandated by the commandment found in Deuteronomy 6:4–9 (the Shema): “And thou shalt write them upon the doorposts of thy house and upon thy gates.” This passage, along with a portion from Deuteronomy 11:13–21, is inscribed on a tiny scroll (the klaf) housed in a small case. The container is usually wooden, ceramic, or metal, and contains the letter shin (the first letter of El Shaddai, “God Almighty”).
Implicit in the act of affixing a mezuzah to the doorpost is the sentiment that the spirit of Godliness will permeate the home and all who reside therein. Furthermore, the words in the mezuzah resonate with the central precepts of Judaism — the unity of God, the love of God, the importance of tradition, and the transmittal of these values to one's children. Following precepts in the Talmud, some Jewish families affix a mezuzah to the doorpost of each room (except the bathroom and kitchen). When leaving or entering the house, many Jews will touch the mezuzah and then kiss the fingers that touched it.
Do people remove the mezuzot when they move?
Since a mezuzah must be treated with reverence, you should take it with you. However, if you know that a Jewish family is moving in and that it will be treated with respect, you should leave it attached.