This week's issue is in memory of a measure of purity lost from the Jewish people. When we besieged Shmuel Hanavi to give us a king, we angered him. This week we made ourselves our own Martin Luther King or John Kennedy. When Hashem decided to destroy Sodom, Amorah, and nearby towns, Avraham pleads on their behalf.
Dirt is something which has no useful form.
It could, in the future, have one, if you grow plants in it, or make something out of pottery or glass. Ashes are the remains of something that once may have had a useful form, but no longer does. The Beis Haleivi continues by pointing out how well the reward fits the deed. The Afar Sotah are used to reveal that the woman had a pure past, that no sin was committed. The Parah Adumah purifies you for the future.