And do not fear those who kill the body but cannot kill the soul. Rather fear him who can destroy both soul and body in hell (Mt 10:28).
This is a prooftext for "traditionalists" and annihiliationists alike. It poses prima facie problems for both. But it's more problematic for annihilationism.
i) This is a prooftext for substance dualism. By itself, the Greek word for "soul" (psyche) doesn't mean an immortal, immaterial soul. But here you have a contrastive relation. In the context of martyrdom, executioners can harm the body, but they can't harm the soul. That's out of their reach.
ii) Implied in the passage is the postmortem persistence of consciousness. The body without the soul is dead, but the soul without the body survives. Persecutors can't touch the real inner you. That contrast is essential to the thought. And that contradicts physicalist annihilationism.
iii) This, in turn, involves a second contrast: humans can only harm a part of the person whereas God can harm the whole person. Persecutors only have power to harm the body, but God has the power to harm the entire individual. Hence, we should fear divine judgment more than martyrdom.
iv) Annihilationists lay great stress on the "destroy" part. But why does Jesus begin with "kill," then switch to "destroy"?
a) Because the second sentence envisions a postmortem situation after the body was killed. That's what makes it a postmortem situation. So it would be incongruous to use the same verb ("kill") in both situations. You can't kill a body that's already dead.
But that means Jesus replaces "kill" with "destroy" to avoid superficial incoherence. The shift in verbs isn't meant to convey a major conceptual distinction. Rather, he changes the verb to make it more consistent with a postmortem situation, as well as divine judgment of the entire individual.
b) Likewise, you can kill a body, because it's a physical organism. But you can't kill a soul, because it's not physical, and it's not "alive" in the biological sense of the word.
c) Moreover, the image of destroying a dead body in hades is figurative. It's not as if dead bodies are teleported to hades. In reality, bodies are buried, and undergo progressive disintegration. In reality, it's the separation of body and soul, when the soul finally "leaves" the body, that causes or results in death. So we're dealing with picture language, as if the embodied decedent passes into the netherworld.
(Although it's possible that this alludes to the general resurrection. But the passage is too terse to confirm that.)
v) Furthermore, the body/soul language is a merism to express the fact that God punishes the entire individual.
vi) Hence, the passage is consonant with the traditional view of eternal punishment.
vii) Taken by itself, the passage is consonant with dualist annihilationism. That, however, requires the cumbersome idea that God recreates the bodies of the damned in order to destroy their bodies (along with their souls) all over again.