In Revelation, to understand the Beast rising out of the "Sea" and the Beast coming up out of the earth, we need to be aware that "Sea" and "Earth" have been symbolically used throughout the Bible.

Psalm 65:7
Which stilleth the noise of the seas, the noise of their waves, and the tumult of the people.

Psalm 93:
3 The floods have lifted up, O Lord, the floods have lifted up their voice; the floods lift up their waves.
4 The Lord on high is mightier than the noise of many waters, yea, than the mighty waves of the sea.

Isaiah 17:12
Woe to the multitude of many people, which make a noise like the noise of the seas; and to the rushing of nations, that make a rushing like the rushing of mighty waters!

Isaiah 60:5
Then thou shalt see, and flow together, and thine heart shall fear, and be enlarged; because the abundance of the sea shall be converted unto thee, the forces of the Gentiles shall come unto thee.

Jeremiah 6:23
They shall lay hold on bow and spear; they are cruel, and have no mercy; their voice roareth like the sea; and they ride upon horses, set in array as men for war against thee, O daughter of Zion.

Isaiah 17:13
The nations shall rush like the rushing of many waters: but God shall rebuke them, and they shall flee far off, and shall be chased as the chaff of the mountains before the wind, and like a rolling thing before the whirlwind.

Ezekiel 26:3
Therefore thus saith the Lord God; Behold, I am against thee, O Tyrus, and will cause many nations to come up against thee, as the sea causeth his waves to come up.

Revelation 17:15
And he saith unto me, The waters which thou sawest, where the whore sitteth, are peoples, and multitudes, and nations, and tongues.

Just as in these verses, in Luke 21, with the same language, the Lord Jesus Christ also used symbolically: "the sea and the waves roaring". The Sea is the Symbolism for the Gentiles, Nations and the Earth is the Symbolism for the Land of Israel.

Luke 21:
25 And there shall be signs in the sun, and in the moon, and in the stars; and upon the earth distress of nations, with perplexity; the sea and the waves roaring.

Psalm 24:2
For he hath founded it upon the seas, and established it upon the floods.

Isaiah 59:19
So shall they fear the name of the Lord from the west, and his glory from the rising of the sun. When the enemy shall come in like a flood, the Spirit of the Lord shall lift up a standard against him.

Jeremiah 46
7 Who is this that cometh up as a flood, whose waters are moved as the rivers?
8 Egypt riseth up like a flood, and his waters are moved like the rivers; and he saith, I will go up, and will cover the earth; I will destroy the city and the inhabitants thereof.

Jeremiah 47:2
Thus saith the Lord; Behold, waters rise up out of the north, and shall be an overflowing flood, and shall overflow the land, and all that is therein; the city, and them that dwell therein: then the men shall cry, and all the inhabitants of the land shall howl.

Isaiah 8:
7 Now therefore, behold, the Lord bringeth up upon them the waters of the river, strong and many, even the king of Assyria, and all his glory: and he shall come up over all his channels, and go over all his banks:
8 And he shall pass through Judah; he shall overflow and go over, he shall reach even to the neck; and the stretching out of his wings shall fill the breadth of thy land, O Immanuel.

Daniel 9:26
And after threescore and two weeks shall Messiah be cut off, but not for himself: and the people of the prince that shall come shall destroy the city and the sanctuary; and the end thereof shall be with a flood, and unto the end of the war desolations are determined.

Genesis 1:2
AND THE EARTH WAS WITHOUT FORM, AND VOID; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.

Jeremiah 4:
22 For my people is foolish, they have not known me; they are sottish children, and they have none understanding: they are wise to do evil, but to do good they have no knowledge.
23 I BEHELD THE EARTH, AND, LO, IT WAS WITHOUT FORM AND VOID; and the heavens, and they had no light.
24 I beheld the mountains, and, lo, they trembled, and all the hills moved lightly.
25 I beheld, and, lo, there was no man, and all the birds of the heavens were fled.
26 I beheld, and, lo, the fruitful place was a wilderness, and all the cities thereof were broken down at the presence of the Lord, and by his fierce anger.
27 For thus hath the Lord said, The whole land shall be desolate; yet will I not make a full end.
28 For this shall the earth mourn, and the heavens above be black; because I have spoken it, I have purposed it, and will not repent, neither will I turn back from it.

Genesis 1:10
And God called the dry land Earth; and the gathering together of the waters called the Seas: and God saw that it was good.

Revelation 21:1
And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea.