What will it look like when that fourth angel (Rev. 18:1) coming with great authority and illuminating the earth with his glory?

Where does this great authority come from?
We have, in Matthew 28:18-19 Jesus saying: "All authority has been given to Me in heaven and on earth Go therefore and make disciples ......"

Jesus has all authority-- He will give that authority to all who proclaim His truth.
So if we see this fourth angel in Rev. 18:1 as God's committed people, that would mean it is Jesus' authority, and the authority of His truth that enable's God's people to proclaim this truth with conviction and great power. That authority and power can only happen when those proclaiming the message totally believe the message, and are fully relying on Christ to give them the words to speak and actions to take, relying on the power and direction of the Holy Spirit, and the convincing authority of truth .