I'm agree with wolfman85 about blood was considered sacred in the bible. But I was reading this article of why the obsession of the Israelites of the use of blood:
"Why was such care taken to drain every drop of blood from the sacrificial animals for no other purpose than to dispose of it in various ways on the main altar of the temple. Why this strange, barbaric obsession with blood in such an apparently theologically sophisticated group of people? There were three reasons for the taboos associated with blood and its ritual disposal in ancient Israel.
First, like many people with animist and semi-animist beliefs, the Israelites held that the nephesh, the life of a human being or an animal, lay in its blood. Every living creature had a nephesh. This nephesh was its life-breath, its spirit, that strange life force that pervaded its body and so kept it alive. When a human being or an animal lost its blood, this lifepower would go out from it, and its flesh would die. The Israelite priests described this connection between the nephesh and the blood in four ways:
a. The blood is the life (Deut 12:23);
b. The life of any flesh (any animate creature) is its blood (Lev 17:14b );
c. The life of any flesh is its blood as its life (Lev 17:14a );
d. The life of any flesh is in the blood (Lev 17:11).
Both the Israelites and Canaanites agreed that vitality and blood belonged together in some way. Yet they differed radically in their consequent use of the blood taken from animals. Whereas the Canaanites quite commonly ate meat with blood in it, because they held that the blood in it was spiritually energizing and life-giving, the Israelites refused to eat meat with blood in it. This taboo against the consumption of blood was based on their refusal to assimilate the spirit of the animal and imbibe any life-power from it (Deut 12:23). The Lord, the God of Israel, had in fact forbidden the consumption of blood by his people. They were allowed to eat meat with the blood drained out of it, but the consumption of blood was strictly proscribed at the pain of excommunication by God himself (Lev 17:10; cf. 7:27). Under no circumstances could the Israelites eat meat with blood in it (Gen 9:4; Lev 7:26; 17:12, 14; Deut 12:16, 23-25; 15:23). It was impossible for the Israelites to gain supernatural life-power from animals by the consumption of their blood.
The second reason for exclusive use of blood in the sacrificial ritual was to prevent its misuse in other popular non-Israelite rituals. Some of the Canaanites slaughtered animals and poured out the blood on the graves of their ancestors as food for their spirits. In return they secured protection, vitality and good luck from their ancestors (cf. Ps 16:3, 4). First-born male animals were also sacrificed in such a way that their blood was given to the earth and the underground deities residing in it. In this way the Canaanites gained good crops for themselves and fertility for their animals (cf. Lev 17:5, 6). Blood was even offered up to demons to appease them (Ps 106:34-39; cf. Deut 32:17) and as nourishment to ghosts to conjure them up for the purpose of divination by augury or necromancy (Lev 19:26; cf. Isa 57:5-10; 65:3-7). In each of these cases blood was used ritually to secure something supernatural, such as vitality, protection, blessing, power, or knowledge. All these ritual practices were eliminated by two divine commands. On the one hand, the Lord instructed the Israelites to bring their burnt offerings and peace offerings to the central sanctuary and to offer them to him only there at his altar (Deut 12:20-25). Anybody who offered a sacrifice anywhere else was treated as a murderer and excommunicated from the people of Israel (Lev 17:1-9; cf. Lev 7:27; Deut 12:26, 27). On the other hand, the Lord also decreed that all the blood from the sacrificed animals should be poured out there on his altar (Lev 17:6; Deut 12:27). It could not under any circumstance be used anywhere else and for any other purpose.
The third and most important reason for the taboo on the consumption of blood lay in the Lord‟s mandate for its use in the rite of atonement. The Lord had forbidden any other human use for the blood of animals so that it could be used only by him for the benefit of his people. Leviticus 17:11 has this singular decree: the life (nephesh) of the flesh is in the blood; and I myself have given it to you for making atonement for your lives (nephashoth) upon the altar; for it is the blood that atones by means of the life (nephesh).
Thus the taboo on the consumption of blood resulted form the divine institution of the rite of atonement as part of daily sacrificial ritual at the tabernacle and, later, at the temple. The Hebrew idiom in Leviticus 17:11 is most arresting. In the ritual texts of the Pentateuch the priests are often said to „give‟, or „place‟, the blood on the horns of the altar (eg. Exod 29:12; Lev 8:15; 9:9; 16:8 etc). Elsewhere the Lord uses the same form of the verb nathan in the first person as here to make a formal endowment of some portion from the offerings to the priests as their due and stipend (Lev 6:10; 9:34; Num 18:8, 11, 12, 19, 21, 24, 26). But in Leviticus 17:11 the Lord does not use this idiom to grant the blood of animals to the Israelites as food for them. Instead, he institutes the ritual use of blood as the means by which both they and he made atonement for their lives. He grants them atonement through the blood placed on the altar by them. This word in Leviticus 17:11 founded the rite of atonement as a sacramental enactment. That word did not merely announce what he would accomplish for them in that rite; it actually empowered the rite, so that he worked atonement for his people through their faithful performance of it. That atonement was granted by means of the blood which was placed on the altar. So, by divine decree, the blood of sacrificed animals could no longer be used directly by the Israelites to boost their vitality but was reserved exclusively for the enactment of atonement."
Kleinig, J. (1999). The Blood for Sprinkling Atoning Blood in Leviticus and Hebrews. Lutheran Theological Journal, 33, 3, 124-135.
As you notice, blood in ancient times was used in liturgical rites for purification and atonement, because it was considered the life giver. Today, thanks for the medical advances and knowledge of human body, people can live despite great blood loss, and people can die even if there is no blood loss (poisoning, electrocution, bacteria/viruses, etc.)
