"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" refers to a valley outside of Jerusalem where trash and dead bodies of animals and criminals were burned when Jesus was on earth. In Gehenna, the "worm is not deceasing" and "the fire is not going out" until it accomplishes the job of destroying the garbage or the 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)
While on earth, Jesus preached only to ISRAEL about the restoration of the Kingdom of Israel in the land promise Abraham, Isaac, and Jacob. He told them that for their Kingdom to be restored to them they needed to repent 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 their 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 of the soul. God is able to resurrect souls from "Gehenna" to 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 verse to teach eternal conscious torment in hell will one day be "ashamed" to have threatened humans with eternal conscious torment. They themselves 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. When they do so, they will reign with Jesus and not be ashamed when He returns.
"For whosoever may be wanting to save his soul will be destroying it, yet whoever shall be destroying his soul on account of Me and of the evangel will be saving it...For whosoever may be ashamed of Me and My words in this generation...the Son of Mankind also will be ashamed of him whenever He may be coming in the glory of His Father." (Mark 8:35-38)
"For whosoever may be wanting to save his soul will be destroying it, yet whoever shall be destroying his soul on account of Me and of the evangel will be saving it...For whosoever may be ashamed of Me and My words in this generation...the Son of Mankind also will be ashamed of him whenever He may be coming in the glory of His Father." (Mark 8:35-38)