In this verse we find these instructions: "And do not fear those who kill the body but cannot kill the soul. But rather fear Him who is able to destroy both soul and body in hell" (Matthew 10:28). This verse is not understood by many because the word "soul" has lost its true meaning. Once that is restored, Jesus' statement becomes clear.
The English word "soul" is a translation of the Greek word psuche and from the Hebrew word nephesh. Both words mean "a living, breathing creature," referring to man or animal. "Soul" never means something immortal inside of man or animal. The words "immortal soul" appear nowhere in the Bible. In fact, the Bible shows that a soul can perish. Ezekiel twice writes, "The soul who sins shall die" (Ezekiel 18:4, 20). The word "soul" pertains to the life of any physical being or creature. Soul simply means "life."
The word translated "life" in Leviticus 17:11 comes from the same Hebrew word translated "soul." This verse can just as accurately be rendered, "For the soul of the flesh is in the blood." Jesus gave His "life" (translated from the same Greek word rendered "soul") as a ransom for us (Mark 10:45) by pouring out His soul - His life's blood - in payment for sin (Isaiah 53:12). Again, "soul" refers to the physical life of human beings or animals.
God can destroy the physical body and the soul (life). Matthew 10:28 tells us that no man can do both. Jesus says the same thing at another time: "And I say to you, My friends, do not be afraid of those who kill the body, and after that have no more that they can do. But I will show you whom you should fear: Fear Him who, after He has killed, has power to cast into hell [the Lake of Fire, the second or final death]; yes, I say to you, fear Him!" (Luke 12:4-5). Man can destroy a physical life, but that results only in the first death (Hebrews 9:27).
God, on the other hand, has the power both to impart life and to take it away, either temporarily or forever. He can resurrect those whom men have killed. He can also kill in a way no man can. If God judges a person to be unworthy of His Kingdom, that person will be thrown into the Lake of Fire to be utterly consumed. This is the second death, from which there can be no resurrection (Revelation 20:14-15; Malachi 4:1). The body and life (soul) of the unrepentant will be destroyed forever.
So, then, what Jesus says is that we should not shape our lives by any threat men may pose against us. We should live our lives in total obedience to God and His laws (see Acts 5:29). If men kill us, it will be only temporary. If God kills us, it will be forever.