This is the only Parsha in the Torah, after Moshe Rabainu was born, that his name does not appear. The Zohar explains that this is not a coincidence.
After B’nei Yisroel worshiped the Golden Calf Moshe begged Hashem to forgive them. He begged so strongly that he told Hashem that if H. didn’t forgive them then “erase me from Y.ur books”. Even though that Hashem did forgive Bnei Yisroel, Moshe’s words were so potent that the curse that Moshe put on himself actually took hold and, therefore, his name “was erased” from our parsha.
Zera Shimshon asks why is his name not mentioned specifically in this parshah and not in some other parsha?
He begins his answer by pointing out that it is in this parsha that Aharon was inaugurated to be the Cohen Gadol.
Let us now understand why was Aharon chosen to be Cohen Gadol and not Moshe?
When Hashem appeared to Moshe at the Burning Bush (sneh) to appoint Moshe to take B’nei Yisroel out of Mitzrayim, Moshe didn’t immediately agree. Hashem punished Moshe for this hesitation and Moshe forfeited the right to be Cohen Gadol.
Why, though, did he not accept the position right away?
The answer is that Moshe knew that if Hashem would redeem them without the help of a mortal man then the redemption would be complete and we would never go back again into Galus. He felt that the servitude that we suffered in Mitzrayim fully purified us and therefore Bnei Yisroel deserved to be redeemed by Hashem alone without him.
Hashem, on the other hand, knew that we were not yet fully pure and therefore we would need to go back into galus to finish the purification process. H. therefore precisely wanted that a mortal man, like Moshe, would take them out of Mitzrayim.
Therefore, if we never sinned again then Moshe would have been proved correct (that we our bondage in Mitzrayim purified us from the Yetzer Haro) and it would not be considered a sin that he hesitated to lead Clal Yisroel. I then follows that Moshe should be the Cohen Godal.
However when we worshipped the Golden Calf we see that the Yetzer Haro was still in us and therefore Moshe sinned and Moshe didn’t deserve to be the Cohen Godal.
And since Aharon merited to be Cohen Gadol only because of Moshe’s sin, Moshe’s curse, which took hold because of that sin, took effect in the same parsha!
According to this we can answer another question.
The Rishonim say that “a curse on condition (if something is done) is effective (if that thing is not done) only if there is at least a smattering of an avairo. If there is not any avairo at all the curse will not take effect. According to this, what even minute sin did Moshe transgress when he davvened for for the forgiveness of Bnei Yisroel that allowed the curse to take effect?
According to what we said before, though, we can answer simply. Since Moshe’s sin was made apparent at the time of the Golden Calf therefore the curse, even though it was made only on condition that Bnei Yisroel wasn’t forgiven, was able to take hold (answer to second question).