Thank you for the feeling question on the Bible, “What is the most frightening book of the Bible?”
There are two “frightening” books of the Bible. They are Revelation and (Isaiah/Jeremiah).
Many readers will say Revelations for the judgments of God that will fall upon the earth that causes destruction and death. It is frightening to read of God’s wrath upon mankind. However, one must keep in mind that the destructions and deaths are brought about by God because of the responses of humans. It is God bringing forth justice on the earth against the wick individuals/people in this world. Even in the midst of destruction and death, God is still gracious by having 144,000 witnesses and the two witnesses proclaiming repentance and forgiveness. Sadly, most of the world would continually ignore God’s message until the final battle at Armageddon.
The Book that is frightening is Isaiah and Jeremiah. It’s devastation that was to come on Israel by the Assyrians and the Babylonians. To think that the Jewish people would eat their own children to survive is horrific since starvation was that terrible. Destruction and death came to the Northern Kingdom and later to the Southern Kingdom. It’s even more frightening to read that God brought this judgment on his own people for their rebellious and callous hearts and mind. Despite God sending his prophets, the leaders and people rejected them. The curses record in Deuteronomy was brought on them as they went into exile from the Promised Land. It is a solemn reminder that God’s people must not think that God will overlook sin in his followers. God is gracious and his patience has a limit for God may well refine his own people through persecution or diseases. The closing of churches is God’s manner in which his people are being exiled and left to their emptiness. The Scriptures are warnings and lessons from which believers are to learn from previous generations and from the Scriptures.
SUMMARY: God does not take delight in disciplining his people nor the nations for their sinfulness. God’s judgment is just and yet there is mercy for those who repent.
For more perspectives:
https://www.quora.com/What-is-the-most-frightening-book-of-the-Bible