And four great beasts came up from the sea, diverse one from another.

Wesley's Notes

7:3 Four great beasts - That is, four great monarchies, great, in comparison of particular kingdoms; beasts for their tyrannical oppressions.

Jamieson-Fausset-Brown Bible Commentary

3. beasts-not living animals, as the cherubic four in Re 4:7 (for the original is a different word from "beasts," and ought to be there translated, living animals). The cherubic living animals represent redeemed man, combining in himself the highest forms of animal life. But the "beasts" here represent the world powers, in their beast-like, grovelling character. It is on the fundamental harmony between nature and spirit, between the three kingdoms of nature, history, and revelation, that Scripture symbolism rests. The selection of symbols is not arbitrary, but based on the essence of things.

Matthew Henry's Concise Commentary

7:1-8 This vision contains the same prophetic representations with Nebuchadnezzar's dream. The great sea agitated by the winds, represented the earth and the dwellers on it troubled by ambitious princes and conquerors. The four beasts signified the same four empires, as the four parts of Nebuchadnezzar's image. Mighty conquerors are but instruments of God's vengeance on a guilty world. The savage beast represents the hateful features of their characters. But the dominion given to each has a limit; their wrath shall be made to praise the Lord, and the remainder of it he will restrain.