When Hashem charged Moshe with the mission of redeeming of the Jewish people, he told him, “V’sham’u l’kolecha…”(3:18), guaranteeing that the people would listen to and believe in Moshe. Yet, Moshe was not satisfied and he insisted that he would not be listened to or believed (4:1):
וַיַּעַן מֹשֶׁה, וַיֹּאמֶר, וְהֵן לֹא-יַאֲמִינוּ לִי, וְלֹא יִשְׁמְעוּ בְּקֹלִי:
In response, Hashem taught Moshe the signs of the staff turning into a snake, water changing to blood, and his hand becoming leprous and then changing back.
Question: once Hashem had guaranteed that the people would listen to and believe Moshe, why did Hashem need to teach Moshe these signs as proof? Hashem could have simply reiterated in response to Moshe that the people would indeed believe.
R’ Tzadok (Pri Tzadik) answers that it was Moshe’s question which introduced the possibility of doubt into the equation. We live up to expectations. Because Moshe did not believe that the people would accept him, this became a self-fulfilling prophecy which undid Hashem’s guarantee, and now he had a need for proof. (See R’ Tzadok for an explanation of why Moshe did not accept Hashem’s guarantee – can G-d guarantee belief, or is it a matter of our collective free choice?)
While on the topic of the parsha, let me just tack on here that there is a Rabeinu Bachye on the pasuk “Va’ta’al shav’asam es haElokim” which mentions a halacha in his parshanut which is quoted by poskim. R’ Bachye says that the word “yisbarach” should not be separated from the precedeing sentence of “yehei she’mei rabbah… l’olam u’lulmei ulmaya”. Of course, there are those who disagree.