Hebrews 9:13, 18, 26

Under the old system, the blood of goats and bulls and the ashes of a heifer could cleanse people’s bodies from ceremonial impurity.

That is why even the first covenant was put into effect with the blood of an animal.

If that had been necessary, Christ would have had to die again and again, ever since the world began. But now, once for all time, he has appeared at the end of the age to remove sin by his own death as a sacrifice.