On Promoting Devotion to the Most Precious Blood of Our Lord Jesus Christ – Inde a Primis (Latin meaning: From the very beginning). Pope John XXIII 1960

In a letter on the devotion to which July is dedicated, the Precious Blood of Jesus, Pope St. John XXIII provides an excellent example of how to encourage the modern person to traditional devotional practice.
In 1960 Pope St. John XXIII wrote the apostolic letter Inde a Primis, encouraging devotion to the Precious Blood of Jesus. The text of the letter follows a typical framework of papal documents of the time, taking the reader through the history of the Church’s belief or practice of the subject. After noting the Roman Church’s centuries-long encouragement of devotion to the Precious Blood, and its spread by the 19th-century priest St. Gaspar del Bufalo, Pope St. John tells us what the devotion has meant to him. It’s not often we get glimpses into the personal piety of the popes themselves!
In the letter, Pope St. John reveals that this particular devotion was central in his upbringing. He recounts how his own parents “used to recite the Litany of the Most Precious Blood every day during July.” Such an example illustrates the Church’s conception of the family as “the domestic church,” as the place where faith is first and primarily nurtured and grown. 
Pope St. John then looks at the life of Christ and points to the many moments in which the Precious Blood appears. Christ’s blood was shed at his circumcision, in the Garden of Gethsemane, and in the tortures of his Passion and Crucifixion—the crown of thorns, the nails, the spear in his side. This spilling
of blood, as the First Letter of St. Peter notes, is salvific: “You know well enough that your ransom was not paid in earthly currency, silver or gold; it was paid in the precious blood of Christ.” (1 Peter 1:17-19, emphasis added) We can easily forget that the title of this devotion comes from Scripture itself!

To read more click here: https://aleteia.org/2019/07/28/when-pope-st-john-xxiii-brought-us-into-his-
childhood-home-to-promote-a-centuries-old-devotion/
Papal Encyclical - On Promoting Devotion to the Most Precious Blood of Our Lord Jesus Christ:
https://www.papalencyclicals.net/john23/j23pb.htm