For this reason, the laws of the פָרָה אֲדֻמָה are referred to as the חֻקַּת of the whole תּוֹרָה (As is explained in Likkutei Torah). This is because in the practical rituals and laws of the פָרָה אֲדֻמָה there are both aspects of רָצוֹא וָשוֹב – of advancing and of retreat in a revealed way. The רָצוֹא is the burning of the heifer and the שוֹב is as the Possuk writes וְנָתַּן עָלָיו מַּיִם חַּיִים אֶׁל־כֶּׁלִי “it shall be placed in a vessel filled with spring water”.
However, there is a deeper concept of רָצוֹא וָשוֹב within the Mitzvah of פָרָה אֲדֻמָה besides the burning of the heifer and placing it in the water, but within the burning itself there are also these two aspects of רָצוֹא וָשוֹב. One aspect is that the heifer gets burnt which is an ascent from below to above akin to רָצוֹא for two reasons: Firstly, it is being burned using ‘fire’ and the nature of fire is to ascend upwards from below to above and secondly the heifer becomes consumed by the fire which is akin to the expiration from below to above another aspect of רָצוֹא. The second aspect relates to the ashes which remain in existence and are not consumed by the fire. These can be viewed as שוֹב a return and a ‘Hamshocha’ into the world. This is also why the ashes of a burnt heifer can be used to purify someone who is impure with ‘Tumas Mes’.
