Follow The Straight Path

Rashi at the beginning of Chukas says that the parah adumah is a kapparah for the sin of the agel.  Why is parah adumah a kapparah for the sin of the agel?  Why is the the derash of זאת התורה אדם כי ימות באהל, אין דברי תורה מתקיימין אלא במי שממית עצמו עליה stuck in the middle of the parsha of tumas meis?  

עשה האלקים אֶת⁠־הָאָדָ֖ם יָשָׁ֑ר וְהֵ֥מָּה בִקְשׁ֖וּ חִשְּׁבֹנ֥וֹת רַבִּֽים.  Mankind was made straight and it is sin that makes man crooked.  The sin of Adam was in calculating that it was better to eat the עץ הדעת.  It was following man's twisted logic.  Since man ruins himself the consequence is death.  It is only with death that he can reach his tikkun.  The same thing happened again at Mattan Torah.  At Sinai פסקה זוהמא (Shabbat 146a,) the sin of Adam was repaired.  But again man made a calculation and was wrong and the sin of the agel brought death back (see Avodah Zarah 5a.)  

At what point was the זוהמא removed?  The Abudarham cites an interpretation on the Haggadah that it happened when Klal Yisrael came to Sinai and that's what the Haggadah means אלו קרבנו לפני הר סיני ולא נתן לנו את התורה דיינו because at that point the זוהמא ended.  What triggered the end of the זוהמא was the plain straight emunah that Klal Yisrael had.  The נעשה ונשמע brought back to the level of הָאָדָ֖ם יָשָׁ֑ר, following in the straight path without calculations.  That is why the kapparah for the agel is through following the חוק of parah, for following through without question.  

The Rambam at the end of Shmettih V'yoval says ולא שבט לוי בלבד אלא כל איש ואיש מכל באי העולם אשר נדבה רוחו אותו והבינו מדעו להבדל לעמוד לפני י"י לשרתו ולעובדו לדעה את י"י והלך ישר כמו שעשהו האלקים ופרק מעל צוארו עול החשבונות הרבים אשר בקשו בני האדם הרי זה נתקדש קדש קדשים.  The return to the level of הָאָדָ֖ם יָשָׁ֑ר and removal of the הֵ֥מָּה בִקְשׁ֖וּ חִשְּׁבֹנ֥וֹת רַבִּֽים it accomplished through the learning of Torah.  It is by removing one's own ego, one's one thoughts and striving to understand the Torah of Hashem, to attach one's self to the straight path, that is accomplished through learning and is the antidote to the original decree of death on mankind.  By fulfilling death in learning, one is able to fix the law of death by killing one's self in learning (based upon a shmuz by R' Elefant.)