But you shall not eat flesh with its life, that is, its blood. I certainly will require your lifeblood; from every animal I will require it. And from every person, [d]from every man as his brother I will require the life of a person.
Genesis 9:4-5 (NASB)
There’s all kinds of interesting interpretations about lifeblood and eating things with the blood in it, but Rabbi Shlomo Yitzchaki (aka “Rashi”), who lived between 1040 and 1105 gives a very simple explanation and application.
בשר בנפשו FLESH WITH THE SOUL THEREOF [SHALL YE NOT EAT] — He here prohibited to them אבר מן החי the eating of a limb cut from a living animal, that is to say that בשר בנפשו (literally, flesh together with its life) means so long as its life is in it you shall not eat the flesh.
Rashi on Genesis 9:4:1
Basically, “don’t limb the animal and eat the limb while the animal is still alive.” It’s not like a plant where you can cut a branch and the plant grows more branches. Animals are different.
And this seems intended to prevent cruelty and suffering for the animals.