What is a mezuzah scroll?
This is the scroll that is put inside the mezuzah cases. It contains the Jewish prayer, the Shema, beginning with the phrase: "Listen, Israel, the Lord is our God, the Lord is One." Mezuzah cases are placed on entry doors to fulfill the Biblical commandment to proclaim the Shema "on the doorposts of your house and on your gates."
What makes a mezuzah scroll kosher?
It is traditionally believed that the Mezuzah scroll protects the household members physically and spiritually. It is the scroll, not the case, that is the essential holy part. Therefore it should be clearly handwritten by a professional Israeli scribe (called a Sofer Stam in Hebrew) on a Kosher animal parchment. All these criteria make the scroll kosher.