There will be weeping and gnashing of teeth in that place, when you see Abraham, Isaac, Jacob, and all the prophets in the kingdom of God, but yourselves thrown out.
Luke 13:28
There will be weeping and gnashing of teeth because there will be two responses to finding oneself in hell. The first response will be great grief, a grief like nothing anyone has ever had on earth. And, second, the other response will be extreme rage unlike anything ever worked up by humanity.
Jesus is speaking to a Jewish audience who felt that all but the worst of them would make it to heaven. Several times in His ministry Jesus preached against this false doctrine. This was not primarily meant to upset His hearers, but to wake them to their lost souls.
Heavenly Father, You are so amazing! Each day I live I understand more of how wonderful you are! I will forever be amazed by You, Almighty God. Thank You for creating us, and for new life in Christ. In the Name of the Lord Jesus Christ I pray and praise You, Amen.