http://revach.net/article.php?id=4332

Section:  Avodah   Category: Olam HaTorah
Parshas Bishalach: Rav Yaakov Kaminetzky - The Para Aduma Is Great Preparation For Matan Torah
Rashi in Parshas Bishalach (15:25) tells us that in Marah, before Matan Torah, Hashem gave the Bnei Yisroel the mitzva of Para Aduma.  Why is this mitzva singled out (as well as the mitzva of Shabbos) to be taught before the rest of the Torah, especially considering that it is relevant to Tumah and Tahara and there was no Mishkan yet?

Rav Yaakov Kamenetzky answers that Torah is unlike any other subject in the world.  It predated the universe and is beyond human comprehension.  We can only comprehend Torah, not based on our own intellect, but rather as a gift from Hashem.  This in itslef is a hard lesson to understand but vital in order to properly learn Torah.  Surely Bnei Yisroel needed training before Matan Torah to understand how to approach Torah, and how different it is then any other subject matter.  There was no better place to start teaching Bnei Yisroel this lesson than by learning about the Para Aduma.  Para Aduma is one of the perplexities of the Torah.  It doesn't make sense from a logical point of view that something can be Mitaher the Timei'im yet be Mitamei the Tihorim.  

With this Sugya, Bnei Yisroel were taught that Hashem's commandments don't need reconciliation with human logic. Lesson 1 in Torah 101 was about the Para Aduma, in order to set the minds straight.  Thereafter, everything we learn, we must understand that even when the Torah says something that makes perfect sense to our logic, our stamp of approval is not needed in any way.  It is Hashem's will and Hashem's way, and that is what counts.