Then I saw three evil spirits that looked like frogs; they came out of the mouth of the dragon, out of the mouth of the beast and out of the mouth of the false prophet.

And I saw three unclean spirits - They assumed a visible form which would well represent their odiousness - that of frogs - but still they are spoken of as "spirits." They were evil powers, or evil influences (Revelation 16:14, "spirits of devils"), and the language here is undoubtedly designed to represent some such power or influence which would, at that period, proceed from the dragon, the beast, and the false prophet.

Like frogs - βατράχοι batrachoi, this word does not occur in the New Testament except in the passage before us. It is properly translated frogs. The frog is here employed clearly as a symbol, and it is designed that certain qualities of the "spirits" here referred to should be designated by the symbol. The frog is characterized as a symbol:

For its rough, harsh, coarse voice

On this account, as a symbol of complaining or reproaching

As a symbol of empty loquacity

As a symbol of heretics and philosophers, as understood by Augustine

Because the frog has its origin in mud, and lives in mud, as a symbol of those who are born in sin, and live in pollution

Because the frog endures all changes of the season cold and heat, summer, winter, rain, frost - as a symbol of monks who practice self-denial

Because the frog though abstemious of food, yet lives in water and drinks often, as a symbol of drunkards

As a symbol of impudence

Because the frog swells his size, and distends his cheeks, as a symbol of pride

How many or few of these ideas enter into the symbol here, it is not easy to decide. We may suppose, however, that the spirits referred to would be characterized by pride, arrogance, impudence, assumption of authority; perhaps impurity and vileness, for all these ideas enter into the meaning of the symbol. They are not here, probably, symbols of persons, but of influences or opinions which would be spread abroad, and which would characterize the age referred to. The reference is to what the "dragon," the "beast," and the "false prophet" would do at that time in opposing the truth, and in preparing the world for the great and final conflict.

Out of the mouth of the dragon - One of which seemed to issue from the mouth of the dragon. On the symbolic meaning of the word "dragon," see the notes on Revelation 12:3. It, in general, represents Satan, the great enemy of the church; perhaps here Satan under the form of paganism or paganism, as in Revelation 12:3-4. The idea then is, that, at the time referred to, there would be some manifestation of the power of Satan in the pagan nations, which would be bold, arrogant, proud, loquacious, hostile to truth, and which would be well  represented by the hoarse murmur of the frog.

And out of the mouth of the beast - The papacy, as above explained, Revelation 13. That is, there would be some putting forth of arrogant pretensions; some loud denunciation or complaining; some manifestation of pride and self-consequence, which would be well represented by the croaking of the frog. We have seen above (notes on Revelation 16:5-6), that although the fifth vial was poured upon "the seat of the beast," the effect was not to crush and overthrow that power entirely. The papacy would still survive, and would be finally destroyed under the outpouring of the seventh vial, Revelation 16:17-21. In the passage before us we have a representation of it as still living; as having apparently recovered its strength; and as being as hostile as ever to the truth, and able to enter into a combination, secret or avowed, with the "dragon" and the  "false prophet," to oppose the reign of truth upon the earth.