To understand why Christianity is a “bloody religion,” we must go back to God’s declarations regarding blood in the Old Testament: “the life of the flesh is in the blood” (Leviticus 17:11, 14). Here God tells us that life and blood are essentially one and the same. The blood carries life-sustaining nutrients to all parts of the body. It represents the essence of life. In contrast, the shedding of blood represents the shedding of life, i.e. death.
Blood is also used in the Bible to represent spiritual life. When Adam and Eve sinned in the Garden of Eden by disobeying God and eating fruit of the forbidden tree, they experienced spiritual death immediately, and physical death years later. God’s warning, “You shall not eat of the tree of knowledge of good and evil. For in the day that you eat of it you shall surely die” (Genesis 2:17) was fulfilled. Their blood—their lives—were now tainted by sin. In His gracious plan, however, God provided a “way out” of their dilemma by declaring that sacrifices of blood, first the blood of animals and finally the blood of the Lamb of God (Jesus Christ), would be sufficient to cover the sin of fallen mankind and restore us to spiritual life. He instituted the sacrificial system, beginning with the animals He himself killed to provide the first garments, thereby “covering” the sin of Adam and Eve (Genesis 3:21). All the Old Testament sacrifices which followed from then on were temporary ones, needing to be repeated over and over. These continual sacrifices were a foreshadowing of the one true and final sacrifice, Christ, whose blood shed on the cross would pay the penalty of sin forever. His death made any further bloodshed unnecessary (Hebrews 10:1-10).
As far as Christianity being a bloody religion, it is. But it is uniquely a bloody religion. Contrary to bloodless religions, it takes sin seriously, indicating that God takes sin seriously and gives a death penalty for it. Sin is not a small matter. It is the simple sin of pride that turned Lucifer into a demon. It was the simple sin of jealousy that caused Cain to slay Abel, etc. And in Adam and Eve eating the forbidden fruit, they believed the deceiver over a good and loving God, choosing to rebel against His love and denying the goodness of His character. Christianity is a bloody religion because it views sin as a holy God views it—seriously.
Also, because God is just, sin requires a penalty. God cannot merely forgive in mercy until the demands of justice have been met. Thus the need for a sacrifice before forgiveness is possible. The shedding of the blood of animals, as Hebrews points out, could only "cover" sin for a time (Hebrews 10:4) until the intended and sufficient sacrifice was made in Christ’s atoning death. Thus, Christianity is different from other bloody religions in that it alone provides a sufficient sacrifice to take care of the sin problem.
Last, although Christianity presents a bloody sacrifice in these regards, it is the only religion that is bloodless in the end. The opposite of death is life. In Jesus’ death, He brought life as is shown in so many verses. And in trusting Christ and His atoning sacrifice for one’s sins, one is saved from death and has passed into life (John 5:24; 1 John 3:14). In Him is life. All other paths lead to death (Acts 4:16; John 14:6).