Jesus used Gehenna as an illustration of what hell would be like (Matthew 10:28; Mark 9:47–48) because it served as a place to discard trash and teamed with burning sewage, flesh, and garbage. Its foul smell quickly repelled any visitors. Its hideous and vile sight complete with maggots and other death-debris, coupled with its history as a place of human sacrifice and false-god worship, gave it a true-life picture of torment.
Gehenna – What is it?
The literal word refers to a geographic location. Gehenna is the Greek form of the Hebrew word ge-hinnom, or the "Valley of the Son of Hinnom." This valley, south of Jerusalem, served as a place where Israelites once sacrificed their children to the Canaanite god Molech (2 Chronicles 28:3; 33:6; Jeremiah 7:31; 19:2–6). In Isaiah 30:33 we see this same place called "Tophet" (translated as "a burning place" in the ESV).
God's hatred of Molech and the worship practices associated with him, compelled God to warn the Israelites that judgment would come upon them if they turned their attentions and worship to the false god (Leviticus 18:20). God said that the valley would no longer be called "Tophet" or the "Valley of the Son of Hinnom," but "the Valley of Slaughter" (Jeremiah 7; 19).
Israelites in Judah did not heed God's warning and were taken into captivity for 70 years by the Babylonians. When they returned to the Promised Land, they began using the valley to burn discarded trash and other undesirable items such as the bodies of criminals, animals, and other items far from places where people lived (2 Kings 23:10).
It is this picture that Jesus used to illustrate hell—a place where those who were judged guilty would be sent to burn forever, suffer stench and devouring worms and other carrion—far from where people live.
It is the word Gehenna He uses in Mark 9:43–48 that is translated most often as "hell."
"And if your hand causes you to sin, cut it off. It is better for you to enter life crippled than with two hands to go to hell, to the unquenchable fire. And if your foot causes you to sin, cut it off. It is better for you to enter life lame than with two feet to be thrown into hell. And if your eye causes you to sin, tear it out. It is better for you to enter the kingdom of God with one eye than with two eyes to be thrown into hell, 'where their worm does not die and the fire is not quenched.'"
What are the distinctions among sheol, hades, hell, the lake of fire, paradise, and Abraham's bosom?
Abraham's bosom – What is it?
Is paradise the same thing as heaven? What is paradise?
Is hell real? Is hell really forever?
How can I be sure that when I die I will go to heaven?
Truth about Eternity