"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 Gehenna.” (Matthew 10:28 CLNT)
"Gehenna" was a valley outside of Jerusalem where trash and dead bodies of animals and criminals were burned in the time of Jesus. In Gehenna, the worm did not stop feeding and "the fire" did not go out until they accomplishes the job of consuming the trash or carcass.
"And if your hand should ever be snaring you, strike it off. It is ideal for you to be entering into life maimed, rather than, having two hands, to come away into Gehenna, into the unextinguished fire where their worm is not deceasing and the fire is not going out." (Mark 9:43-44)
Jesus preached to ISRAEL about the restoration of their Kingdom in the land promised to Abraham, Isaac, and Jacob. He told them that their kingdom would not be restored until they repented of their sins.
"Thenceforth begins Jesus to be heralding and saying, Repent! for near is the kingdom of the heavens!...teaching in their synagogues and heralding the evangel of the kingdom." (Matthew 4:17,23)
Jesus presented Himself to Israel as the Messiah who would restore the kingdom of Israel. Jesus said they need not fear the Romans who might kill the body but had no control over the soul. God is able to make alive again souls cast into "Gehenna" and then reign with Him in the kingdom.
"And the souls of those executed because of the testimony of Jesus and because of the word of God, and those who do not worship the wild beast or its image, and did not get the emblem on their forehead and on their hand- they also live and reign with Christ a thousand years. The rest of the dead do not live until the thousand years should be finished." (Revelation 20:4-5)
Those who use the above verses to teach eternal conscious torment in the hell of Greek mythology will one day be "ashamed" to have done sot. Some of them may miss out on the reign of Christ "until the thousand years should be finished".
Believers should not fear death at the hands of the governments of men, they should entrust both body and soul to God the Father and His Son, the Lord Jesus Christ.