The month of July is dedicated to the Precious Blood of Jesus. The Catholic Church dedicates each month of the year to certain devotions.
The feast of the Precious Blood of our Lord was instituted in 1849 by Pope Pius IX. The devotion is as old as Christianity.
The Blood of Christ refers to the physical blood shed by Jesus Christ primarily on the Cross, and the salvation which Christianity teaches was accomplished thereby. It can also refer to the sacramental blood (wine) present in the Eucharist or Lord's Supper.
The Church makes this dedication because it is important for us to contemplate the mystery of the Eucharist, which contains the life blood of our faith and the Church.