And you shall command . . . (27:20)
Tetzaveh is the only Parshah in the Torah since Moses' birth in which Moses' name does not appear (with the exception of the book of Deuteronomy, which consists mostly of a first-person narrative spoken by Moses). The reason for this is that [when the people of Israel sinned with the golden calf,] Moses said to G‑d: "If You do not [forgive them], erase me from the book that You have written" (Exodus 32:31). This was realized in the Parshah of Tetzaveh, since the censure of a righteous person, even if made conditional on an unfulfilled stipulation, always has some effect.
(Baal HaTurim)
This being the Shabbat before Purim, on which we celebrate the foiling of Haman the Amalekite's plot to destroy the Jewish people, the weekly Parshah is supplemented with the Zachor reading (Deuteronomy 25:17-19) in which we are commanded to remember the evil of Amalek and to eradicate it from the face of the earth.
"Parshat Zachor" is the second of four special readings added during or immediately before the month of Adar (the other three being "Shekalim", "Parah" and "Hachodesh")