three unclean spirits
These are spirits of demons. See commentary on Revelation 16:14. See Three: Life, Resurrection, Completeness, the Trinity.
Their comparison with frogs alludes to their uncleanness, being aquatic animals lacking scales (Lev. Lev. 11:9-12; Deu. Deu. 14:9-10). They also recall the plague of frogs in Egypt (Ex. Ex. 8:2-13; Ps. Ps. 78:45; Ps. 105:30). See The Plagues of Egypt and the Tribulation.
They are the elect agents to awaken the world to the attempt to abolish God from the earth; and they are frog-like in that they come forth out of the pestiferous quagmires of the uerse, do their work amid the worlds evening shadows, and creep, and croak, and defile, and fill the ears of the nations with their noisy demonstrations, till they set all the kings and armies of the whole earth in enthusiastic commotion for the final crushing out of the Lamb and all His powers.1coming out of the mouth
The mouth is the organ which reflects the will as evidenced by ones words. Fire of judgment came out of the mouths of the two witnesses (Rev. Rev. 11:5+) and a sword comes out of the mouth of Jesus (Rev. Rev. 1:16+; Rev. 19:15+), the latter undoubtedly a reference to the Word of God (see commentary on Revelation 1:16). That which comes forth from these mouths is empowered, influenced, and promulgated by the unclean spirits. The unclean spirits proceed from the mouths of the unholy triumvirate, suggesting the persuasive and deceptive propaganda which in the last days will lead men to an unconditional commitment to the cause of evil.2
of the dragon . . . of the beast . . . of the false prophet
The three spirits correspond to the three personages of the antitrinity : the dragon, the Beast, and the False Prophet. All three work together with a unified goal of drawing the nations to battle.
The dragon is Satan and the devil , both names which indicate his slanderous accusations (Rev. Rev. 12:9+). When he speaks a lie, he speaks from his own resources, for he is a liar and the father of it (John John 8:44). The Beast is known for his blasphemous mouth (Dan. Dan. 7:8, Dan. 7:11, Dan. 7:20, Dan. 7:25; Dan. 11:36; Rev. Rev. 13:6+) and the False Prophet, although appearing like a lamb, speaks like a dragonHe tells those who dwell on the earth to make an image to the beast (Rev. Rev. 13:11+). Each of these would be highly influential on their own, but aided by unclean spirits, their deception is especially effective. See commentary on Revelation 13:14.
1 J. A. Seiss, The Apocalypse: Lectures on the Book of Revelation (Grand Rapids, MI: Zondervan Publishing House, 1966), 378.