What does Genesis 7:18 mean?

We were told in the previous verse that the floodwaters increased or multiplied. Now we're told that the waters "prevailed." This is from the Hebrew root word gabar. This is a military term, used for winning victory in battle. It can also mean "overwhelmed, overtook, or conquered." Anyone who has seen a flood or tsunami in action knows how much power there is in moving water. Beneath the ark, the flood waters overwhelmed everything on land, while rising higher and higher.

The rise of these waters, in some ways, is a reversal of God's initial creation. In the beginning, God drew dry land out of the water (Genesis 1:9–10). Here, in judgment, He is sending that land back under the waters. This is, in literal action, God "resetting" this aspect of His creation.

Although the waters destroy everything on land, they do not prevail, over the ark. We were told in the previous verse that the boat floated high above its original place on the ground. Now we're told that it floats on the surface of the water. The ark and its inhabitants were on the move. It's worth noting that the ark is actually not a "boat." There are no oars, sails, rudders, or other controls mentioned. It has one purpose: to float above the destruction, and let God take care of the rest.