The Best Way to Live Life

Why is Moshe's name missing from Parshas Tetzaveh, when Bnei Yisrael did teshuva and his request to be erased should no longer have stood? And why this parsha of all of them? A Gemara in Zevachim about Moshe at the burning bush, and another in Shabbos about suspecting others, lead to two ways of serving Hashem. Then the Vilna Gaon sends a messenger to find an esrog, and the only beautiful one in town belongs to a merchant who will sell it on one strange condition. The messenger has no idea how the Gaon will react.