Hell and its fire are real, that’s why Jesus repeatedly warned His listeners of their impending doom and the terrifying place that awaits them if they persist in rejecting Him. Now we will see plenty of verses in the Scripture, describing the fires of Hell that will never end, and is eternal.
43 And if your hand causes your downfall, cut it off. It is better for you to enter life maimed than to have two hands and go to hell—the unquenchable fire, [44 where
Their worm does not die,
and the fire is not quenched.]
46 “And they will go away into eternal punishment, but the righteous into eternal life.”
11 and the smoke of their torment will go up forever and ever. There is no rest day or night for those who worship the beast and his image, or anyone who receives the mark of his name.
10 The Devil who deceived them was thrown into the lake of fire and sulfur where the beast and the false prophet are, and they will be tormented day and night forever and ever.
41 Then He will also say to those on the left, ‘Depart from Me, you who are cursed, into the eternal fire prepared for the Devil and his angels!
I will address, one passage that annihilation people like to go to for teaching that hell is not eternal.
28 Don’t fear those who kill the body but are not able to kill the soul; rather, fear Him who is able to destroy both soul and body in hell.
The word destroy in Greek suggest a state of spiritual death and to be rendered useless. GR. Strong’s #622
Basically, It is saying that the function of the person and their purpose which God made them for, is destroyed since people in Hell will do nothing but weep, and gnash their teeth in severe pain (Luke 13:28). An illustration would be of a shattered light bulb after being slammed to the ground. Its function is destroyed, and it ceases to work as it should, but the broken pieces of glass and its components continue to remain. You cannot say that because the light bulb is destroyed, it has been annihilated.