TT #52 · Parashas Noach · Fourth Aliyah · Passuk 9:6
Whoever sheds the blood of man, by man shall his blood be shed, for in the image of God He made man.
Torah Temimah elaborates the reason for the severity of murder — the divine image.
“For in the image of God He made man” — therefore murder is so severe: one who kills a human diminishes the likeness and the image.
Custom (theological ground for the severity of murder).
Murder is uniquely grave because it reduces the presence of the divine image in the world.