But to the fearful and unbelieving, [and sinners], and those who make themselves abominable, and murderers, and fornicators, and sorcerers, and idolaters, and all liars, their part [is] in the lake which burns with fire and brimstone; which is the second death.
Revelation 21:6 And he said to me, It is done. I am the Alpha and the Omega, the beginning and the end. I will give to him that thirsts of the fountain of the water of life freely.
Revelation 21:7 He that overcomes shall inherit these things, and I will be to him God, and he shall be to me son.
Revelation 21:8 But to the fearful and unbelieving, [and sinners], and those who make themselves abominable, and murderers, and fornicators, and sorcerers, and idolaters, and all liars, their part [is] in the lake which burns with fire and brimstone; which is the second death.
Revelation 21:9 And there came one of the seven angels which had had the seven bowls full of the seven last plagues, and spoke with me, saying, Come here, I will shew thee the bride, the Lamb's wife.
Revelation 21:10 And he carried me away in [the] Spirit, [and set me] on a great and high mountain, and shewed me the holy city, Jerusalem, coming down out of the heaven from God,
The verse centers on "fearful", "unbelieving", "sinners", "make", "themselves", "abominable", "murderers", and "fornicators". It is saying that the verse draws attention to "fearful" and "unbelieving", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 7's "He that overcomes shall inherit these things..." into verse 9's "And there came one of the seven...", so "fearful" and "unbelieving" belong inside that flow. In Revelation context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "fearful" and "unbelieving" with trust shaped by these words, not by a vague optimism outside the passage.