This is the third “hearken” statement. That there were three in a row suggests that this was an intentional set that was to be taken together, and as an escalating idea. This is a poetic technique that underscores the words with a structure that emphasizes them.
In this set we have the culmination of the set of ideas. The first address was to those who “follow after righteousness.” The second was addressed to “my people.” This defines his people as those “that know righteousness, the people in whose heart I have written my law.”
Jehovah tells his people not to fear their enemies, for they shall be destroyed as moths destroy garments.
Verses 9 and 10 are references to very old Israelite stories of Jehovah taming the deep and Rahab, the monster of the deep. The stories are only referenced in the Bible, both here and in Psalm 89:11–13. Clearly those stories were known to Isaiah’s audience, but it is doubtful that they were among the teaching to the New World, although they would have fit well with the New World mythology. The verses are to indicate Jehovah’s power over all of the earth, and that is the intended message for Jacob’s audience, whether they understood the stories behind these verses or not.