On the Shabbat before Purim, many congregations will read Parshat Zachor (Deuteronomy 25:17 - 20). In the three short verses of this parshah, we are commanded not once but twice to recall a dangerous attack on our people: we are told to remember (Zachor) what the Amalekites did to the Israelites after they left Egypt and not to forget (Lo Tishkach).