Leviticus 14:25

The priest shall put the blood — Upon the extremities of the body, to include the whole. And some of the oil was afterwards put in the same places upon the blood. That blood seems to have been a token of forgiveness, the oil of healing: For God first forgiveth our iniquities, and then healeth our diseases. When the leper was anointed, the oil must have blood under it, to signify that all the graces and comforts of the spirit, all his sanctifying influences are owing to the death of Christ. It is by his blood alone that we are sanctified.