Parshas Acharei Mos: Maharal Tzintz - The Blood Of Animals
The Torah tells us at length in three pasukim (Acharei Mos 17:10-12) that we may not eat blood of an animal. It also specifically mentions a Ger explicitly twice. Why?
The Maharal Tzintz explains that the reason why a person cannot consume the blood of an animal is because a person strives upwards towards the heavens, "Ruach Bnei HaAdam HaOlah Hi L'Ma'ala", while an animal is drawn downward to the ground, "V'Ruach HaBeheima HaYoredes Hi L'Matah LaAretz" (Koheles 3:21).
The pasuk says (11) that "Ki Nefesh HaBasar BaDam Hi", the main spirit of the animal is in the blood with which we do not want to weigh ourselves down. One who consumes the blood and brings into himself the animal spirit, will receive Kares (10) because by being drawn down he will literally be cut off from his roots above and will not be able to enjoy the ruchniyus.
However an animal still has sparks of Kedusha and when it goes on the Mizbei'ach those sparks can be drawn out. Therefore says the Torah, even a Ger who may have consumed blood before becoming a Ger, may not consume blood anymore because he can still purify himself.