The blood “drawn from Immanuel’s veins” is blessed blood because it is redemptive blood.
Redemption means “to deliver by payment of a price.” That is what Christ did through His shed blood. His own “precious blood” is the price He paid for our redemption from sin.
The blood of Jesus Christ is the key and center of redemption. It has power to redeem. Everything concerning salvation depends on it. Just as there is no life for the arm severed from the body, so there is no redemption from sin apart from the blood!