Can you tell me the meaning and purpose of the Jewish symbol: the Mezuzah.?

A mezuzah is an ornamental cylinder that is placed on 2/3rds of the way up on a door frame. Inside the cylinder is a scroll with Deuteronomy 6:4 written on it by a professional scribe.

The mezuzah is a symbol of G-d's watchful care over the home and its dwellers. The name of G-d, Sha-dai, which appears on the reverse side of the parchment is an acronym for the Hebrew words which mean "Guardian of the doorways of Israel."

It's a replica of the ten comandments in scroll form! Usually made to hang on a chain around the neck.

The mitzvah to place mezuzot on the doorposts of our houses to keep His words constantly in our minds and in our hearts