We hear mention now in Isaiah of this creature Leviathan which is mentioned in the Psalms as well (Look at Psalm 74:13-14). Leviathan was a creature that represented the sea and everything bad about the sea. Remember, the Israelites were not big fans of the sea, even though they lived right on it. They were not considered a sea-faring civilization. So it makes sense that on judgment day the Leviathan, or the dragon which we read about in Revelation, is defeated by God. Those things that scare us we want to have conquered when we face eternal life where everything is perfect. The defeat of a sea monster would count as a big step toward perfection.
Here is a depiction of it by the mid 19th century artist Gustave Dore.
But we quickly transition from the Leviathan which is mentioned in two verses to Jacob and Israel taking root again, because remember they had been plucked up in a dry and arid land. We find the promise that life will come back. Look at vs.13 and take heart that there will be a day when God will call His people to Him and they will actually respond and come back and worship him on the holy mountain. It speaks specifically of those who were carted off into exile, into slavery really, and will be brought back.