The fire speaks of judgment (Mtt. Mat. 3:11-12; Luke Luke 12:49), just as when the man in Ezekiels vision scattered coals of fire over Jerusalem (Eze. Eze. 10:2).
threw it to the earth
The act of the angel with the censer prefigures the angels with the seven bowls of Gods wrath (Rev. Rev. 16:1+, Rev. 16:3+, Rev. 16:4+, Rev. 16:8+, Rev. 16:10+, Rev. 16:12+, Rev. 16:17+). Here, there is an explicit connection between the petitions of the saints and the resulting judgment, whereas the bowls contain Gods own wrath.1
All this occurs in answer to the prayers of the saints. There are those who think meanly of prayer, and are always asking: What profit should we have if we pray unto the Almighty? (Job Job 21:15.) The true answer is, much every way.
There is an eye that never sleeps
Beneath the wing of night;
There is an ear that never shuts
When sink the beams of light.
There is an arm that never tires
When human strength gives way;
There is a love that never fails
When earthly loves decay.
That eye is fixed on seraph throngs;
That arm upholds the sky;
That ear is filled with angel songs;
That love is throned on high.
But theres a power which man can wield,
When mortal aid is vain,
That eye, that ear, that love to reach,
That listening ear to gain.
That power is PRAYER, which soars on high,
Through Jesus, to the throne;
And moves the hand which moves the world,
To bring salvation down!2
Noises is φωναὶ [phōnai] which can also be translated as voices (ASV, KJV, YLT). It is translated as noises in Revelation Rev. 8:5+ and by sound in Revelation Rev. 9:9+. The noises (or voices), thunderings, lightnings and earthquake are all indicators of judgment. There is a direct cause-and-effect relationship between the prayers of the saints which were mingled in the censer before its contents were thrown to the earth and these indicators of impending judgment. See commentary on Revelation 4:5. These terms compose a FORMULA OF CATASTROPHE; and the fourfold character here denotes universality of the catastrophe in respect to the thing affected.3 See Four: the Entire World, the Earth.
1 Symbolically, this represents the answer to the prayers of the saints through the visitation on earth of Gods righteous judgments.Alan F. Johnson, Revelation: The Expositors Bible Commentary (Grand Rapids, MI: Zondervan Publishing House, 1966), Rev. 8:5.
2 J. A. Seiss, The Apocalypse: Lectures on the Book of Revelation (Grand Rapids, MI: Zondervan Publishing House, 1966), 187.