The original first century audience for John's Apocalypse was in the middle of some of the worst persecution Christians have endured. So this scene cut close to the bone for them. And there was also an overlay of the Temptations of Christ #Revelation13
Minor Prophets: Malachi, Where is the God of Justice?
The Lord’s answer to the cry for justice begins with Messiah, but God’s answer continues with the promise to return and bring just judgment. However, God will begin with God’s own people.
Gospel of John: A Deep Cleanse
Rather than a warning, I see this as rescue and relief. This is a promise we can count on, for that is the true love of God, to cleanse us through and through, that we might become heavenly stuff.