The images of the bloody dagger and the blood on the hands of Macbeth and Lady Macbeth are both symbols of their guilt for the murder of Duncan. The way in which they imagine that the blood is present even after they have washed their hands invokes a sense that the sin they have committed cannot be washed away. In the religious context of the period, blood can represent either guilt or purity. In the Pray of Humble Access in the Book of Common Prayer, the congregation prays:
``Grant us therefore, gracious Lord, so to eat the flesh of thy dear Son Jesus Christ, and to drink his blood, that our sinful bodies may be made clean by his body, and our souls washed through his most precious blood, and that we may evermore dwell in him, and he in us.``
Because Macbeth and Lady Macbeth are not contrite for their act, blood stains rather than purifies, and even hand-washing (as Pontius Pilate washes his hands when Jesus is led away) cannot remove the stain from their souls which is externally symbolized as hands from which imaginary blood cannot be washed.