Psalms 106:38

And shed innocent blood ... - The blood of those who had committed no crime; who did not “deserve” the treatment which they received. That is, they were sacrificed “as” innocent persons, and “because” it was believed that they “were” innocent: the pure for the impure; the holy for the unholy. It was on the general principle that a sacrifice for sin must be itself pure, or it could not be offered in the place of the guilty; that an offering made for one who had violated law must be by one who had “not” violated it. This was the principle on which “lambs” were offered in sacrifice. It is on this principle that the atonement for sin by the Lord Jesus was made; on this depend its efficacy and its value.

And the land was polluted with blood - That is, Either so much blood was thus poured out, that it might be said that the very land was polluted with it; or, the sin itself was so great, that it seemed to defile and pollute the whole land.