I don’t see any difficulty in understanding Jesus to be referring to the casting of a slain Israelite into Hinnom Valley by a Roman soldier during the siege of Jerusalem in 70 A.D. Jesus is likely using the words “body” (soma) and “soul” (psuche) as he does in Mt. 6:25, with the former referring to a person’s outward, physical frame (which can be clothed and stripped naked) and the latter referring to a person’s natural life (which must be sustained by food and water). When killing the soma is contrasted with killing the psuche, the latter means to take a person’s life (cf. Mt 2:10), while the former means to inflict harm upon a person’s body without mortally wounding them. Understood in the larger context of Matthew 10:16-23, Jesus’ words “kill the body” probably refers to what the Jewish persecutors of the early Christian church were allowed to do (i.e., scourge people in the synagogues, without actually taking their lives - cf. John 18:31), while “kill the soul” refers to what those with the authority to execute a person could do.
The expression “destroy both soul and body” was evidently a proverbial saying or figure of speech expressing the visible destruction or wasting away of whatever is in view, whether it be a human being or a king’s forest (see Isaiah 10:18). So for a person to be destroyed “both soul and body” was to undergo the greatest visible destruction that a person could undergo in this world. And would those slain Israelites cast into Hinnom Valley have undergone such fearful, visible destruction? Undoubtedly; left unburied in this valley, they would have wasted away and been consumed by the fires that one would reasonably expect to have been lit by the Romans to deal with the inevitable stench of rotting corpses, while those not yet destroyed by the fires would have provided food for the maggots (or “undying worms”) until nothing resembling the slain individuals remained.
While countless Jews were slaughtered by the Roman army when the nation of Israel was overthrown, Christ’s faithful and watchful followers escaped this fearful calamity by heeding his words to flee the city of Jerusalem when God gave them the opportunity (Matt 24:15-20; cf. Luke 21:20-21). In this way, God protected the early Christians from being destroyed “both body and soul” when he brought judgment upon the corrupt nation of Israel through the instrumentality of the Roman army.
It may be objected that this interpretation of Matthew 10:28 and Luke 12:4-5 demands that the word “kill” (apokteino) be understood in a limited sense. But such an objection is, I believe, invalid. It is evident that soma is being used in a limited sense in Matt 6:25, which is, notably, the only other verse where Christ distinguishes between soma and psuche. Now, if Christ was employing the word soma in Matt 6:25 to embrace every aspect of a person’s self from a physical, biological standpoint, then that which Christ says is sustained by food and drink (the psuche) in Matt 6:25 would necessarily be included in this general, inclusive meaning - for food and drink is necessary to keep our bodies (in the fullest sense of the word) alive. That is, soma, when used in a general sense, necessarily includes that aspect of us which Christ implies is sustained by food and drink, as well as that aspect of us which may be clothed or stripped naked. But because Christ distinguishes between the words soma and psuche by limiting soma to that which may be clothed and stripped naked, and excluding from the meaning of the word that aspect of us which is sustained by food and drink, soma must be understood in a limited sense. Thus, it is not so much apokteino (“kill”) that is to be understood as denoting less than its usual meaning, but soma. In this context, it refers to the outward frame of a person’s body (i.e., that which is clothed), not the body in its entirety.
Moreover, the very fact that soma and psuche are distinguished by Christ in Matt 10:28 (and by implication, in Luke 12:4-5, which is undoubtedly a parallel account) makes it an exception to how the words are used throughout Scripture. The only other place in the NT where psuche is distinguished from soma is in 1 Thess 5:23. But here, pnuema (“spirit”) is distinguished from both soma and psuche - a fact which renders problematic any argument that psuche, when distinguished from soma, denotes some aspect of man’s nature that continues to exist in a disembodied state after death. And Matthew 10:28 (and again, Luke 12:4-5 by implication) is also the only example in the NT where soma is spoken of as being able to be killed or destroyed apart from psuche (or life) necessarily being killed or destroyed as well. This, too, forces us to understand Christ’s use of psuche and apokteino in Matt 10:28 as being exceptions to how the terms are used throughout the NT.
The fact that there is only one other example in all of Scripture in which “body and soul” are spoken of as being “destroyed” (Isaiah 10:16-18), is reason enough for this example to be taken into consideration when seeking to interpret Matthew 10:28 and its parallel in Luke 12. And when we do that, it becomes clear that for body and soul to be “destroyed” is equivalent to what happens when “a sick man wastes away.” Thus, any objection to the word “kill” being understood in a limited sense in Matthew 10:28 and Luke 12:4-5 on the grounds that it would be an exception to the rule overlooks the following facts: 1) that soma is clearly being used in a limited sense in Matthew just a few chapters back, 2) that Christ’s distinguishing between soma and psuche is itself an exception to how the words are used throughout Scripture, 3) that psuche is being used by Christ as the Greek equivalent of the Hebrew nephash, which is often used in the OT to refer to any creature created with a capacity for respiration and sentient existence (Gen 1:20-21, 24-25; 2:7), or to the natural life/vitality of a living, breathing creature (Gen 1:20, 30; 19:17; 35:18; Ex 4:19; 21:23; Lev 17:11-14; 1Sam 22:23; Job 12:10; Esther 7:7; Prov 12:10; Jonah 4:3) and 4) that the only other example in Scripture where “body and soul” are said to be “destroyed” is in Isaiah 10:16-18, which provides no support for the traditional understanding of Matt 10:28.