"And thou shall write them upon the doorposts of thy house and on thy gates." That is the commandment found in the Book of Deuteronomy, Verse 6, line 9. That is the reason for the Mezuzah; the item affixed at an angle to the doorpost of a Jewish home. The Hebrew word Mezuzah actually means doorpost, but over time it has evolved to mean the item and what it contains. Very little about this important object has been left to chance. Including how it is hung. You might ask, just what is it that makes a Mezuzah so important, and why is it hung on the doorpost, and if it is so important, why isn't it hung vertically?
Learn More About A Mezuzah And The Blessing Said When Hanging The Mezuzah, Along With The English Translation Of The Mezuzah Prayer.