‘And the sixth angel sounded, and I heard a voice from the horns of the golden altar which is before God, one saying to the sixth angel who had the trumpet, “loose the four angels who are bound at the great river Euphrates”.'
The voice comes from the horns of the golden altar. This altar is the altar of incense from which the prayers of God's people are offered to God (Revelation 8:3). Thus it is essentially the voice of the people's prayers that has been heard. The altar is ‘before God', where previously it was ‘before the veil' (Exodus 30:6). This is because the veil has been removed in Christ (Hebrews 10:20).
‘Loose the four angels who are bound at the great river Euphrates'. These are not the same as any previously mentioned for they are ‘bound' and need releasing. In all this we see that the powers of evil have been bound by Christ (Mark 3:27 and parallels) and that their release is dependent on His will, and in accordance with His purpose.
The mention of the River Euphrates suggests the sphere of their operations which is the Mesopotamian region. Compare Jeremiah 46:6; Jeremiah 46:10 which refers to a previous ‘day of the Lord' (Jeremiah 46:10) when Nebuchadrezzar, king of Babylon smote the Egyptians at the River Euphrates (Jeremiah 46:2; Jeremiah 46:13; Jeremiah 46:26)). It is beyond the border of the land which God had intended for His people Israel (Genesis 15:18; Deuteronomy 1:7; Deuteronomy 11:24; Joshua 1:4), the land which was once conquered by David (2 Samuel 8:3). The language in Jeremiah 46:10 is very reminiscent of the final days of the Lord's vengeance, but is specifically stated to refer to the days of Pharaoh Necho and King Nebuchadrezzar. (How careful we must be in handling the word of God). It could, however, be seen as a pattern of what is to come, as history repeats itself, for God is unchanging, and to some extent so is man.