The feast of the Most Precious Blood of Jesus was put on the church calendar just in the 19th century. In 1969, it was placed in conjunction with the feast of Corpus Christi. I can see how doing this strengthens the understanding among us that, in Holy Communion, if one receives the Host alone, one receives all of Christ, His Sacred Body, Precious Blood, soul and divinity.
Even in the New Missal, which lacks a separate feast for the Most Precious Blood, there is a Votive Mass of the Precious Blood which can be said anytime the church calendar allows votive Masses to be said.
But, as the Extraordinary Form today follows the 1962 calendar, we can also happily observe this as a separate feast on July 1 and for good reason.
At the Last Supper, Christ consecrated the bread and the wine separately.
There was a reason for this. Namely, death occurs when body and blood are separated. This dual consecration points to the death of Christ on the cross.
And, as with many things in the spiritual, there are other reasons for this separate consecration as well.
"There is no forgiveness without the shedding of blood." (Hebrews 9:22)
The Letter to the Hebrews in the passage just cited is speaking of the Old Testament sacrifices, which were prophetic of the perfect sacrifice yet to come in Christ; a "shadow of the good things" that were still on their way (Hebrews 10:1). Instead, Christ entered the Holy Place (where atonement for sin is obtained) by His own blood (Hebrews 9:12).
This Blood was shed even in His Infancy
(The Circumcision of the Lord)
Saint John tells us, "The blood of Jesus cleanses us from all sin." (I John 1:7) And, again, "To Him who loved us and washed away our sins in His own blood." (Rev 1:5).
So precious is this blood, as the payment for our sins, that when the soldier pierced the lifeless Body of the Lord, His Precious Blood came out separately from His Body (John 19:34).
HOW CAN WE ACCESS THIS PRECIOUS BLOOD?
Saint Paul answers us. When we were baptized, we were baptized into His death (Romans 6:3). The water we use in the Sacrament of Baptism is mystically His Blood which washes us clean of sin. Saint Paul has first-hand knowledge of this truth when he himself converted to Christianity and was told by the holy Ananias, "Arise and be baptized and wash away your sins." (Acts 22:16)
Baptism washes away our sins; Original Sin for everyone; personal sins, in addition, to those baptized at an older age, who have the use of reason and therefore who are capable of committing personal sins.
Baptism has to be the first access we have to the saving and Precious Blood of Jesus, because we cannot access His Blood by any other means until we are born again and made spiritually alive and capable of benefitting from His Blood.
But the second way to access His Precious Blood is in the Holy Sacrifice of the Mass. In Mass, we fulfill His command to "Do this in memory of Me." Do what? To offer the Body which is broken and the Blood which is shed "for the remission of sins." Even before we receive Him in Holy Communion, we are already blessed and graced by assisting at this sublime Sacrifice.
Then, we access His Precious Blood by receiving Him in Holy Communion. As stated already, when we receive the Host, we are receiving the entire Person, including His Precious Blood.
THE BLOOD IS IN THE BODY, THE BODY CONTAINS THE BLOOD
Saint Thomas Aquinas expresses this truth beautifully :
Caro cibus, sanguis potus:
Manet tamen Christus totus,
Sub utráque specie.
The Flesh is food, the Blood drink:
All of Christ remains however
under either form.
Saint Paul knew that the wine that is offered at the Eucharist is no longer wine when we drink It, either through the chalice or when we eat the Host. He taught that if one received Holy Communion unworthily, one would be "guilty of the body and blood of the Lord." (1 Corinthians 11:27)
"The life of the flesh is in the blood."
"Unless you eat My Flesh and drink My Blood, you shall not have life within you."