Leviticus 24:17

And if a man destroy the life of any one of the children of Israel, he shall verily be put to death by the sword.

ואיש כי יכה כל נפש אדם, seeing that among some nations cursing the deity is considered a very minor sin as we know from Isaiah 8,21 והתקצף וקלל במלכו ובאלוהיו, “and he shall rage against his king and his divinity, etc.;” we know from our sages in Sanhedrin 60 that when one hears a gentile blaspheme (even against our G’d) one need not rend one’s garment in mourning over having been a witness to such blasphemy, for if that were not the halachah our garments would consist of innumerable shreds.
Keeping this in mind, we might have assumed that the curse uttered by the blasphemer in our paragraph should have been treated as irrelevant. This is especially so since we are all aware that blaspheming against G’d does not harm Him in any way, is an exercise of man’s frustration, not something harmful to the object of his blasphemy. The Torah explains that the reason why this blasphemy is treated as if something of substance, G’d forbid, must be seen in a different context. We know from Torah legislation that each deliberate act of disobedience against G’d is basically an act of insurrection, mutiny, and we could expect it to be treated as such, i.e. as equivalent to forfeiting one’s life.
Nonetheless, the Torah has demonstrated that some deliberate sins rate quite different punishments than others. Basically, the Torah provides for financial penalties, physical punishment, and the death penalty. Clearly, this proves that G’d views different sins as differing in degree of insurrection, or due to different degrees of provocation experienced by the sinner. Killing a human being, basically deserves the death penalty, i.e. anything less would mean that the killer’s life is worth more than that of his victim. When someone kills an animal, this is not comparable, so that the penalty is financial, restitution to the owner for what he lost.
When someone causes injury (deliberately), if the injury was caused to a fellow human being, by rights, the offender should be punished by bodily punishment, unless he were physically too weak to endure such punishment. Seeing that it is impossible to impose an exact equivalent for the injury caused, the sages decided to substitute a financial penalty instead. We must not think that the offender thereby gets off lightly, as the financial compensation comprises five different categories of harm suffered by the injured party, including even his injured pride. (compare Baba Kamma 83)
When someone injures an animal the financial penalty is considerably milder. When someone causes injury to a human being we also distinguish between one human being and another. If he injured his father or mother, he is guilty of the death penalty, whereas an injury of similar severity to someone else draws only a financial penalty; when he injures an animal it is obvious that the penalty would only be financial. Cursing father or mother is not mentioned in the Torah here as it is in a different category altogether, seeing that this cannot be compared to blaspheming, words which by themselves have no effect, since what can man possibly do to harm G’d?. Parents may be harmed by their children’s curses though not necessarily visibly. [some of the wording is my own. Ed.]