I wrote the following a couple of years ago.
Matthew 10:28 (cf. Luke 12:4-5)
“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.”
Though perhaps an alien concept to most Christians and non-Christians alike, the word here translated “soul” (psuche) is never said or implied in Scripture to refer to an immortal part of man’s nature, and unless this verse is the single exception, the word is never used to denote a part of man that can exist in a disembodied state after death. Far from teaching this, the word psuche is being employed by Christ in the same sense as he uses it in Matthew 6:25 (cf. Matt 2:10):
*Therefore, I tell you, do not be anxious about your life (psuche), what you will eat or what you will drink, nor about your body, what you will put on. Is not life (psuche) more than food, and the body more than clothing? *
Both here and in Matthew 10:28, psuche simply denotes the natural, biological life of a person (which must be sustained by food and water), while soma is being employed by Christ to refer to a person’s physical frame (which can be clothed or stripped naked). With this contrast kept in mind, there is a sense in which one’s “body” (as distinguished from one’s life) can be “killed” without one’s life being “killed” as well. In the former case, severe bodily harm may be inflicted, while the person’s life is spared. But in the latter case, it is the life itself upon which harm is inflicted, which can only result in the total destruction of the person. Thus, when soma (i.e., the physical frame of a person) and psuche (a person’s natural life) are distinguished, the body may be spoken of as being “killed” or “destroyed” without one’s life being “killed” or “destroyed” as well. That this is indeed the case will be even more evident when we consider the first time the expression “destroy both body and soul” is used in Scripture.
To speak of “soul and body” being “destroyed” was evidently a common Jewish expression with which Christ’s disciples were well acquainted. There is no indication that Christ’s disciples misunderstood what he meant by the destruction of “soul and body” in Gehenna." This is evident, because when they did not comprehend his meaning on other occasions, we find them making all the necessary inquiries. But here, they made none. From this single circumstance it is evident that they did not learn the meaning of this expression from Jesus, but that it was instead a common expression and proverb of that day. Now, by comparing Matt 10:28 with Isaiah 10:16-18, we can see that it was used as a proverbial expression denoting the total destruction of anything to which it was applied:
Therefore the Lord GOD of hosts will send wasting sickness among his stout warriors, and under his glory a burning will be kindled, like the burning of fire. The light of Israel will become a fire, and his Holy One a flame, and it will burn and devour his thorns and briers in one day. The glory of his forest and of his fruitful land the LORD will destroy, both soul and body, and it will be as when a sick man wastes away. Isaiah 10:16-18
Here, we find God threatening a national judgment against Assyria, after having judged Israel. The expression under consideration is applied to the destruction of the glory of the king of Assyria’s “forest and fruitful land,” making the expression obviously figurative in this instance. The literal meaning of the expression “destruction of soul and body,” however, seems to refer to that which takes place when “a sick man wastes away.” This agrees with our observation that the “body” could be spoken of as being “killed” (or in this case, “destroyed”) without the “soul,” or life, necessarily being “killed” (or “destroyed”) as well. But when a sick man “wastes away,” his condition is such that both his life and his physical frame are progressively “destroyed” by the illness. Thus, whether this expression is understood figuratively or literally, it has nothing to do with the punishment or annihilation of “immortal souls” in a “disembodied” state of existence.
Moreover, Christ is not talking about a post-mortem judgment when he employs the word that is here and elsewhere translated “hell” in less literal translations of the English Bible. The word he uses is “Gehenna,” which literally means “Valley of Hinnom” in the Greek language, and is the proper name of an actual valley that lies just south of the city Jerusalem. Originally known as “the valley of the sons of Hinnom,” this location is referred to in the Old Testament in the following verses: Josh 15:8, 18:16; 2 Kings 23:10; 2 Chron 28:3, 33:6; Neh 11:30; Jer 7:31, 32, 19:2, 6, 32:35. In most of these verses it is to be understood in its literal sense. But in Jeremiah 19 (cf. 7:30-34) we read that, by God’s authority, the Valley of Hinnom (“Gehenna”) – which was also known as “Topheth” (v. 6) - was made an emblem, or figure, of the temporal calamities which God threatened to bring upon the unfaithful nation of Israel for her sins (v. 12).
Other than its literal and emblematic meaning, no other meaning is ever attached to this word in the inspired Scriptures. Any other meaning one may choose to assign to the word (for whatever reason) is simply without divine sanction and authority. Though for centuries the idea of post-mortem, unending torment has been attached to this word by “orthodox” theologians, this sense is entirely foreign to its inspired meaning as found in Jeremiah 19. To make it refer to a place of endless misery in a future existence (or to any kind of punishment after death) is to completely disregard how it is used and defined in Scripture. Moreover, because Christ gives no indication of introducing a new emblematic meaning to a word whose meaning had long ago been fixed by his own inspired Scriptures, we can confidently maintain that, whenever Christ employs “Gehenna” in a non-literal sense, he is ascribing to it the same emblematic meaning that was assigned to it by God in Jeremiah’s day.
Just as in Jeremiah’s day, a severe judgment upon the nation of Israel was looming over the horizon when Christ spoke these words to his disciples. In Matthew 23:32-36 (cf. 1 Thess 2:15-16; Isaiah 65:6-7), we read of Christ warning the religious leaders of the Jewish nation that, upon their filling up the measure of their fathers’ sins, their generation would be severely punished. No other generation is in view but the one to which Christ spoke. In verse 33 of this passage, Christ refers to this approaching judgment upon that generation as their being sentenced to “Gehenna” (i.e., the Valley of Hinnom). Any Jew familiar with their Hebrew Scriptures would have understood Jesus’ words to be a warning of an impending national judgment, because it is this of which “Gehenna” (or “Topheth,” which was a location within this valley) had become an emblem (again, see Jeremiah 19, whole chapter; cf. chap. 7:30-34). Christ goes on to say (vv. 37-38),
O Jerusalem, Jerusalem, the city that kills the prophets and stones those who are sent to it! How often would I have gathered your children together as a hen gathers her brood under her wings, and you would not! See, your house is left to you desolate…
Here Christ is referring to that terrible judgment that would come upon the guilty nation of Israel. Their capital city, Jerusalem, would be completely overthrown, and their “house” (i.e., the temple) would be left to them “desolate.” This national judgment fell upon the Jewish people like a thunderbolt at the climax of the Jewish-Roman war in 70 A.D., when the Roman army, led by General Titus, sacked the city of Jerusalem and utterly destroyed the temple. More than a million Jews perished during this violent overthrow of the Jewish nation.
So what is Jesus saying in the verse under consideration? There are two possible views. Understood in the larger context of Matthew 10:16-23, Jesus’ words “kill the body” may refer to the bodily punishment which the Jewish persecutors of the early Christian church were allowed to inflict upon people in the synagogues, and stands in contrast with what the Roman authorities had the power to do (cf. John 18:31), and of which they took full advantage at the climax of the Jewish rebellion in 70 AD when countless Jews were slaughtered. But Christ’s obedient and watchful followers escaped this fearful calamity by heeding their Lord’s words to flee the city of Jerusalem and the surrounding area when God gave them opportunity (Matt 24:15-20; cf. Luke 21:20-21). In this way, those Jewish Christians who fled from the impending judgment upon the Jewish nation were spared from being destroyed “body and soul.” when God brought judgment upon the corrupt nation of Israel through the instrumentality of the Roman army.
An alternative (though similar) view is that Jesus is not referring to the literal bodies and lives of individual people, but is using the expression in a figurative sense to refer to the early Church as a corporate whole. “Destroying the body” refers to the intense persecution and death that many Christians suffered prior to the overthrow of Jerusalem. But God would not allow the Church to be utterly destroyed by her enemies (i.e., destroyed both body and soul); as Christ prophesied, the gates of Hades (death) would not prevail against his Bride (Matt 16:18). Thus it could be said that, though persecuted severely, the “soul” or “life” of the Church was spared during this tumultuous time.
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That might be an important doctrinal provision to mention, if so! (And, if so, welcome to our group as the first Mormon commenter I would be aware of, by the way. 
It’s true that the term Gehenna doesn’t show up often in the NT (and all but one time it’s in the Synoptics. The other time the term is used is James 3:6. I’m more than a little doubtful that the meaning assigned there can only be either literal, or else emblematic in the sense you gave. Hopefully this won’t mean that whatever meaning assigned to the word for whatever reason in that case is “simply without divine sanction and authority”! 
). I do not, in fact, believe psuche to only carry the meaning of “natural, biological life.” What I said was this:
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