We learn in chapter 5 of Joshua that while the generation of the Exodus had been circumcised in Egypt, their children and grandchildren born in the desert had not been. And since only the circumcised may eat of the Passover sacrifice, it seems that this ritual too was not maintained during the forty years in the desert. Anyway, we couldn't have eaten matzah in the desert as we had no grain - only manna.
Haman, according to the Scroll of Esther, was a member of the tribe of Amalek. Thus, we learn the consequences of disregarding the Torah commandment to wipe out the memory of Amalek - as long as they are allowed to continue to exist, they remain a threat, the enemy who for no rational reason constantly plots our destruction. And we read the above passage on the Shabbat before Purim every year,