After Moshe warns Pharaoh about מכת בכורות, the text summarizes the מכות:
Why add that last line? We’ve been paying attention for the past 2 weeks; we haven’t missed המפתים האלה!
The next פרשה is the mitzvah of the קרבן פסח:
And Rashi explains that Aharon was part of that mitzvah:
The problem is that this doesn’t seem to be true. ה׳ only gave the mitzvot to Moshe:
In other words, ויאמר ה׳ אל משה ואל אהרן doesn’t mean ה׳ spoke to Aharon; it means ה׳ spoke to Moshe who spoke to Aharon, and together they spoke to בני ישראל. The Taz is very bothered by this:
So the Taz says that ויאמר ה׳…אל אהרן must mean that Aharon got some kind of divine message:
This idea, that a נביא may get a message about another נביא's נבואה, affects the halacha:
ה׳ may allow other נביאים to be witnesses, to “hear” the message given to a נביא. And that, in fact, is why we accept the laws of the Torah: we were witnesses at מעמד הר סיני:
Sforno says that Aharon’s reward for his מסירת נפש in participating in the מכות was to be part of the continuation of those מופתים; the laws of פסח will be the permanent record of their efforts.
But there is another side of this, giving the first mitzvah to Moshe, with Aharon as the “witness”. Aharon had been a נביא long before this:
But from here on, Aharon will not act as a נביא; he will not bring the divine message to בני ישראל. He will become the כהן, which in part involves the עבודה, but also involves being the keeper of the עדות (the לוחות and the first ספר תורה). The כהנים were the witnesses to the Torah:
Which is why the כהנים were involved in teaching Torah:
And in judgment:
The אמירה to Aharon in this parasha is the beginning of his role as the keeper of the עדות for the future.