When someone sins, something or someone has to die (blood must be spilt) to pay for that sin(s) this is why the bible states the penalty of sin is death.
Blood is the fluid of life. Scientist, though they have tried have found it a difficult medium to reproduce. It is made up of water various ions and cells. Blood is in a constant process of supplying our tissue needs on the one hand, and purifying them on the other.
With these protection and cleansing properties in mind, to what extent is blood, the fluid of life, of significance to Christianity?
The King James Version of the Bible mentions the word blood 447 times. The Old Testament mentions it 346 times, and the New Testament 101 times. The lower value in the New Testament might be a reflection of the coming of Jesus, who died for the remission of sins which therefore meant no more sacrificial offerings of bullocks and lambs.
The Old Testament begins with Abel's blood being spilt, and later Moses turning the waters in Egypt into blood. This then turns to the element of protection where the Israelites under the direction of God protected themselves by covering their two side post and the upper post so when God Passed over they would not be harmed.
We then see Moses at a later time sprinkling blood on the altar and on the people for what I believe to be for the purification and cleansing of the Israelites Lev 14:14, Lev 16:18-19. This is then clearly stated in Lev 17:11 - "For the life of the flesh is in the blood: and I have given it to you upon the altar to make an atonement for your souls: for it is the blood that maketh an atonement for the soul". So the significance of the blood for the Christian is for the atonement of our sins.
Jesus in the New Testament on the cleansing aspect of blood mentions in Mat 26:28 - For this is my blood of the New Testament, which is shed for many for the remission of sins. This is why Christians would make the statement "I am covered by the blood of Jesus". The spilling of Jesus' blood was atonement for our sins, and so therefore covered or better yet protected from the consequences of sin which is death. Having said that, does it mean the Christian can go on sinning after being saved? I personally don't think so. Those who sin after this must genuinely ask for forgiveness of sin and he is faithful and just to forgive us 1 Jn 1:6-10.
The book of Acts in relation to blood then states we are to refrain from blood - Acts 15:29 i.e. I believe not to drink it. This might explain why the communion is to be done just in remembrance of him and that we are not drinking his blood; else it probably would be contradictory. Rev 1:5 then goes on to say that Jesus, who is the first begotten of the dead, has washed away the sins of those who have accepted him with his own blood.
In the final analysts when someone sins, something or someone has to die to pay for that sin(s) that is why the bible states the penalty of sin is death, blood must be spilt for a covering. Jesus has therefore paid the price in full for our sins with his death - Heb 9:22-28, from which he has risen and now lives Mar 16:6-9. As a Christian therefore one must believe that the blood of Jesus offers protection and cleansing properties - Rom 3-25.