Because we live in times that are increasingly uncertain and perilous, fear is a reality all will face at some time. A sobering consideration is that fear appears in a list in Revelation 21:8 describing those who will be cast into the Lake of Fire: "But the cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death" (emphasis ours throughout).
As bad as murderers, the sexually immoral, and sorcerers are, note that God puts first, at the head of the line, the cowardly and unbelieving. The Bible in Basic English renders these first few words as, "But those who are full of fear and without faith. . . ." Why are fear and lack of faith such preeminent sins in God's eyes?
Before answering that question, let us first establish that fear and a lack of faith are sins. Notice Nehemiah 6:10-14:
Afterward I came to the house of Shemaiah the son of Delaiah, the son of Mehetabel, who was a secret informer; and he said, "Let us meet together in the house of God, within the temple, and let us close the doors of the temple, for they are coming to kill you; indeed, at night they will come to kill you." And I said, "Should such a man as I flee? And who is there such as I who would go into the temple to save his life? I will not go in!" Then I perceived that God had not sent him at all, but that he pronounced this prophecy against me because Tobiah and Sanballat had hired him. For this reason he was hired, that I should be afraid and act that way and sin, so that they might have cause for an evil report, that they might reproach me. My God, remember Tobiah and Sanballat, according to these their works, and the prophetess Noadiah and the rest of the prophets who would have made me afraid.
Nehemiah labels fear as sin. Romans 14:23 says the same of unbelief: "But he who doubts is condemned if he eats, because he does not eat from faith; for whatever is not from faith is sin." A lack of faith is also sin.
So, why are they at the beginning of the list in Revelation 21:8? And, of the two, why is fear first? The New Living Translation provides an answer to that question by rendering the verse's opening words as, "But cowards who turn away from me. . . ." In fear, cowards run from the battle, showing disloyalty to their sovereign. In the spiritual realm, they put their self-interest above everything, including God. Fear violates the first commandment by not giving God the preeminence it demands. It is not surprising, then, that the first sin listed is the one that so directly violates that first great commandment (Matthew 22:36-38).
In his commentary on Revelation 21:8, James Burton Coffman notes, "But it is not of natural fear and timidity that John speaks; it is that cowardice which in the last resort chooses self and safety before Christ." He nails the core problem of fear—at the end, it can cause us to reject God in favor of self.