If scripture says so, then it's true. The Bible teaches that blood sacrifice is necessary for the atonement of sin. Abel's sacrifice was accepted because it was a blood sacrifice. All such sacrifices that were instituted under the law of Moses pointed to the ultimate sacrifice of God's Son for the propitiation of sin.
11 For the life of the flesh is in the blood, and I have given it to you upon the altar to make atonement for your souls; for it is the blood that makes atonement for the soul.’ Leviticus 17:11
16 For where there is a testament, there must also of necessity be the death of the testator. 17 For a testament is in force after men are dead, since it has no power at all while the testator lives. 18 Therefore not even the first covenant was dedicated without blood. 19 For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and goats, with water, scarlet wool, and hyssop, and sprinkled both the book itself and all the people, 20 saying, “This is the blood of the covenant which God has commanded you.” 21 Then likewise he sprinkled with blood both the tabernacle and all the vessels of the ministry. 22 And according to the law almost all things are purified with blood, and without shedding of blood there is no remission. Hebrews 9:16-22
