Ezekiel 18:4
Ezekiel 18:44Behold, every soul belongs to Me; both father and son are Mine. The soul who sins is the one who will die.
— "the soul that sins is the one that will die" — is a central Watchtower proof-text for soul mortality. If souls can die, the Watchtower argues, they cannot be immortal and must cease to exist at physical death. This is paired with ("man became a living soul") to argue that the soul is simply the whole person, not a separable part.
Jesus himself distinguishes between what can and cannot be done to the soul. (NWT): "Do not become fearful of those who kill the body but cannot kill the soul; but rather be in fear of him who can destroy both soul and body in Gehenna." Two categories of agents, two categories of reach. Men can kill the body; men cannot kill the soul. Only God can destroy both. and fit together cleanly: the soul is not intrinsically immortal (God can destroy it), but it is not killed when the body dies (men cannot reach it). The Watchtower's reading collapses the categories — if soul = body = life, then killing the body would kill the soul, and contradicts itself. Jesus's distinction preserves both verses. The soul survives the body's death; only God has authority over its final state.