So you shall not pollute the land in which you are: for blood defiles the land: and the land cannot be cleansed of the blood that is shed therein, except by the blood of him that shed it.
Read Chapter 35
George Leo Haydock
Defile not. To inspire a greater horror for murder, the earth was represented as defiled by blood, and only to be purified by the death of the criminal. Without shedding of blood, there is no remission, Hebrews ix. 22. (Haydock)
On the same principle, our churches, are deemed profane, when murder, or some great indecencies, have been committed in them, so that they require a fresh consecration. (Calmet)