What is "Gehenna"?
Hell is the place of eternal punishment prepared for the wicked, for the devil and his angels (Matthew 25:41), and those who do not know God (2 Thessalonians 1:8), and those who do not obey the gospel (2 Thessalonians 1:8).
What is the punishment?
These shall be punished with everlasting destruction from the presence [literally, "the Face"] of God and from the glory of His power. (2 Thessalonians 1:9)
The hand of the LORD referred to the divine inspiration for prophets, which is the Spirit of God. (Ezekiel 1:3)
The glory of the LORD refers to God in all His fullness, especially as He interacts with man. (Exodus 33:18)
Psalm 52:11 Do not cast me away from Your presence, and do not take Your Holy Spirit from me.
Psalm 88:4-5 I am counted with those who go down to the pit; I am like a man who has no strength, adrift among the dead, like the slain who lie in the grave, whom You remember no more, and who are cut off from Your hand.
Psalm 88:14 LORD, why do You cast off my soul? Why do You hide Your face from me?
The absence of God's presence is the same as the absence of His Spirit.
What is Hell like?
There will be wailing and gnashing of teeth (Matthew 8:12; 13:42, 50; 22:13; 24:51; 25:30), reflecting the remorse for lost opportunity.
Scripture
Matthew 7:21-23
Matthew 10:28
Matthew 12:33-37
Matthew 12:50
Matthew 16:26-27
Matthew 24:30
Matthew 25:14-30
Matthew 25:31-46
Conclusion
Let us hear the conclusion of the whole matter:
Fear God and keep His commandments (Matthew 19:17; Matthew 22:34-40), for this is man's all. For God will bring every work into judgment, including every secret thing, whether good or evil. (Ecclesiastes 12:13-14)
Responsibility
See then that you walk circumspectly not as fools but as wise, redeeming the time, because the days are evil. (Ephesians 5:15-16)
Therefore do not be unwise, but understand what the will of God is. (Ephesians 5:17)
The wise use of gifts and abilities entrusted to us results in greater opportunities, while their neglect results not only in the loss of more opportunities, but of that which was entrusted to us.
Jesus said, "Not everyone who says to Me, 'Lord, Lord, shall enter the kingdom of heaven, but he who does the will of My Father in heaven.'" (Matthew 7:21)
Good Character
The return of the Lord will usher in judgment, which will divide people. The judgment will be based on moral character, and the character is revealed by charitable deeds or the lack of them.
Jesus said, "But when you do a charitable deed, do not let your left hand know what your right hand is doing, that your charitable deed may be in secret; and your Father who sees in secret will Himself reward you openly." (Matthew 6:3-4)
Conclusion
Jesus said, "The law and the prophets were until John. Since that time the kingdom of God has been preached, and everyone is pressing into it." (Luke 16:16)
Since John the Baptist announced that repentance and belief were the means of entrance into the kingdom.
Belief
Jesus said, "And this is the will of Him who sent Me, that everyone who sees the Son and believes in Him may have everlasting life, and I will raise him up at the last day." (John 6:40)
Repentance
Jesus said, "but unless you repent you will all likewise perish." (Luke 13:3, 5)
2 Peter 3:9 The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance.