Jesus is the perfect Lamb of God who has no blemish. Our atonement may only come from someone who does not deserve the punishment. In other words, Jesus cannot take our punishment if He also deserves punishment (otherwise, He will have to die twice, once for Himself and once for us). Isaiah rightly prophecies that the atoning sacrifice of the Lamb of God is made with an innocent Lamb without a blemish. He is pure, holy, and righteous.