I belong to an internet forum in which a thread is titled "Please Don't Post to this Thread" Naturally, the most random things are posted. My reply was that "We shall post upon this thread, and upon our doorposts, and upon our gates". While I sat in my chair quite pleased with my Biblical response, I took a second look at our mezzuzah. Then it dawned on me.
In Exodus, lamb's blood was placed on the doorposts of the Hebrew slaves, signifying that the people in those homes belonged to the Lord. He then passed over those houses during the plague of the firstborn while slaughtering the first-born males of all other households. Poor lambs would have to slaughtered daily in order to post blood as a reminder that the firstborn of Israel were redeemed However, the mezzuzah is a more permanent reminder that 1) we were once slaves to sin 2) we were bought with the price of the Lamb of G-d 3) redemption is for all who are willing. 4) G-d's laws are for each generation and a mezzuzah can be passed down for several generations as reminder that we serve the G-d of our fathers.