It is not a sin to donate blood or have a transfusion. The Bible does not talk about blood transfusion because this medical procedure did not exist when it was written. Blood transfusion is not eating blood.
The value of blood
In the Bible, blood symbolizes life and is treated with respect. Animal blood was used as a sacrifice to God, to pay for sins. In addition, eating blood was often part of pagan rituals that God detested. Therefore, Jews were forbidden to eat blood.
In the New Testament, Jesus taught that all foods are pure to eat before God ( Mark 7: 18-19 ). On the other hand, the apostles left the recommendation not to eat blood, probably because of their association with pagan practices.
Find out here: can a Christian eat blood?
Blood transfusion – is it allowed?
A blood transfusion is very different from eating blood. Eating implies that food is processed by the digestive system. Transfusion is direct transfer of compatible blood to the veins, without digestion. There is no procedure that resembles this in the Bible.
More than blood, the Bible considers human life to be sacred ( Genesis 1:27 ). Life must be protected. Blood transfusion has already saved many lives, without breaking any ethical rules of the Bible. The person who receives the blood has a new opportunity to live and serve God. The value of life must be placed above fear of possibly breaking a ceremonial rule that does not affect spiritual life.
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Blood is precious and very important for the life of the body. Therefore, it is wrong to shed blood for ritual or religious reasons ( Leviticus 19:28 ). But donating blood is not for that purpose. Donating blood serves to save someone else’s life.
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Jesus, when he died on the cross, gave all his blood to save us. This was an incredible act of love. Likewise, Jesus said that the greatest expression of love is when someone gives his life for someone else ( John 15: 12-13 ). When someone dies saving a person, he is considered a hero. Donating blood is like donating a little bit of your life to save someone.