This week’s Parsha, תצוה, is the only Parsha from שמות until the end of the Torah that does not have Moshe’s name in it.
The classical answer as to why this is the case, is because when Moshe pleaded with Hashem to forgive the Jewish people for the sin of the Golden Calf, he gave a threat to Hashem. He said that if the Jews were not forgiven, then,”erase my name from Your book.” He was not erased entirely but was erased from פרשת תצוה.
The Vilna Gaon gave a different reason for Moshe’s name not appearing. He said that there was a connection with this Parsha and Moshe’s Yahrtzeit, as it always falls close to the seventh of Adar, the day that Moshe died.(Wednesday night and Thursday is the seventh of Adar.) His name being erased, may be a hint to his ultimate demise.
A third answer could be that it was in this week’s Parsha, it became official that Moshe was erased from being the Kohein Hagadol. He served in that capacity for seven days before the Mishkan dedication. After this, the position was handed over to his brother Aharon. Interesting explanations as to why Moshe’s name does not appear in our Parsha.